provider/aws: `aws_spot_fleet_request` throws panic on missing subnet_id (#8217)

or availability_zone

Fixes #8000

There was a hard coded panic in the code!!!

```
panic(
				fmt.Sprintf(
					"Must set one of:\navailability_zone %#v\nsubnet_id: %#v",
					m["availability_zone"],
					m["subnet_id"])
			)
```

This was causing issues when we set neither an availability zone or a subnet id.
This has been removed and is now handled with an error rather than a panic.

This was what happened with the new test before the fix:

```
=== RUN   TestAccAWSSpotFleetRequest_brokenLaunchSpecification
panic: Must set one of:
availability_zone ""
subnet_id: ""
goroutine 129 [running]:
panic(0x11377a0, 0xc8202abfc0)
	/opt/boxen/homebrew/Cellar/go/1.6.2/libexec/src/runtime/panic.go:481 +0x3e6
github.com/hashicorp/terraform/builtin/providers/aws.hashLaunchSpecification(0x11361a0, 0xc8202e07e0, 0xc800000001)
	/Users/stacko/Code/go/src/github.com/hashicorp/terraform/builtin/providers/aws/resource_aws_spot_fleet_request.go:953 +0x685
github.com/hashicorp/terraform/helper/schema.(*Set).hash(0xc82005ae00, 0x11361a0, 0xc8202e07e0, 0x0, 0x0)
	/Users/stacko/Code/go/src/github.com/hashicorp/terraform/helper/schema/set.go:180 +0x40
github.com/hashicorp/terraform/helper/schema.(*Set).add(0xc82005ae00, 0x11361a0, 0xc8202e07e0, 0xc820276900, 0x0, 0x0)
```

The test then ran fine after the fix:

```
% make testacc TEST=./builtin/providers/aws TESTARGS='-run=TestAccAWSSpotFleetRequest_brokenLaunchSpecification'
==> Checking that code complies with gofmt requirements...
/Users/stacko/Code/go/bin/stringer
go generate $(go list ./... | grep -v /terraform/vendor/)
2016/08/16 08:03:18 Generated command/internal_plugin_list.go
TF_ACC=1 go test ./builtin/providers/aws -v -run=TestAccAWSSpotFleetRequest_brokenLaunchSpecification -timeout 120m
=== RUN   TestAccAWSSpotFleetRequest_brokenLaunchSpecification
--- PASS: TestAccAWSSpotFleetRequest_brokenLaunchSpecification (32.37s)
PASS
ok  	github.com/hashicorp/terraform/builtin/providers/aws	32.384s
```

Full test run looks as follows:

```
% make testacc TEST=./builtin/providers/aws TESTARGS='-run=TestAccAWSSpotFleetRequest_'                     ✹
==> Checking that code complies with gofmt requirements...
/Users/stacko/Code/go/bin/stringer
go generate $(go list ./... | grep -v /terraform/vendor/)
2016/08/16 08:04:34 Generated command/internal_plugin_list.go
TF_ACC=1 go test ./builtin/providers/aws -v -run=TestAccAWSSpotFleetRequest_ -timeout 120m
=== RUN   TestAccAWSSpotFleetRequest_basic
--- PASS: TestAccAWSSpotFleetRequest_basic (33.78s)
=== RUN   TestAccAWSSpotFleetRequest_brokenLaunchSpecification
--- PASS: TestAccAWSSpotFleetRequest_brokenLaunchSpecification (33.59s)
=== RUN   TestAccAWSSpotFleetRequest_launchConfiguration
--- PASS: TestAccAWSSpotFleetRequest_launchConfiguration (35.26s)
=== RUN   TestAccAWSSpotFleetRequest_CannotUseEmptyKeyName
--- PASS: TestAccAWSSpotFleetRequest_CannotUseEmptyKeyName (0.00s)
PASS
ok  	github.com/hashicorp/terraform/builtin/providers/aws	102.648s
```

builtin/providers/aws/resource_aws_spot_fleet_request.go

@@ -290,6 +290,13 @@ func resourceAwsSpotFleetRequest() *schema.Resource {
 
 func buildSpotFleetLaunchSpecification(d map[string]interface{}, meta interface{}) (*ec2.SpotFleetLaunchSpecification, error) {
 	conn := meta.(*AWSClient).ec2conn
+
+	_, hasSubnet := d["subnet_id"]
+	_, hasAZ := d["availability_zone"]
+	if !hasAZ && !hasSubnet {
+		return nil, fmt.Errorf("LaunchSpecification must include a subnet_id or an availability_zone")
+	}
+
 	opts := &ec2.SpotFleetLaunchSpecification{
 		ImageId:      aws.String(d["ami"].(string)),
 		InstanceType: aws.String(d["instance_type"].(string)),
@@ -938,12 +945,6 @@ func hashLaunchSpecification(v interface{}) int {
 		buf.WriteString(fmt.Sprintf("%s-", m["availability_zone"].(string)))
 	} else if m["subnet_id"] != nil && m["subnet_id"] != "" {
 		buf.WriteString(fmt.Sprintf("%s-", m["subnet_id"].(string)))
-	} else {
-		panic(
-			fmt.Sprintf(
-				"Must set one of:\navailability_zone %#v\nsubnet_id: %#v",
-				m["availability_zone"],
-				m["subnet_id"]))
 	}
 	buf.WriteString(fmt.Sprintf("%s-", m["instance_type"].(string)))
 	buf.WriteString(fmt.Sprintf("%s-", m["spot_price"].(string)))

builtin/providers/aws/resource_aws_spot_fleet_request_test.go

@@ -3,6 +3,7 @@ package aws
 import (
 	"encoding/base64"
 	"fmt"
+	"regexp"
 	"testing"
 
 	"github.com/aws/aws-sdk-go/aws"
@@ -33,6 +34,20 @@ func TestAccAWSSpotFleetRequest_basic(t *testing.T) {
 	})
 }
 
+func TestAccAWSSpotFleetRequest_brokenLaunchSpecification(t *testing.T) {
+	resource.Test(t, resource.TestCase{
+		PreCheck:     func() { testAccPreCheck(t) },
+		Providers:    testAccProviders,
+		CheckDestroy: testAccCheckAWSSpotFleetRequestDestroy,
+		Steps: []resource.TestStep{
+			resource.TestStep{
+				Config:      testAccAWSSpotFleetRequestConfigBroken,
+				ExpectError: regexp.MustCompile("LaunchSpecification must include a subnet_id or an availability_zone"),
+			},
+		},
+	})
+}
+
 func TestAccAWSSpotFleetRequest_launchConfiguration(t *testing.T) {
 	var sfr ec2.SpotFleetRequestConfig
 
@@ -208,6 +223,51 @@ resource "aws_spot_fleet_request" "foo" {
 }
 `
 
+const testAccAWSSpotFleetRequestConfigBroken = `
+resource "aws_key_pair" "debugging" {
+	key_name = "tmp-key"
+	public_key = "ssh-rsa AAAAB3NzaC1yc2EAAAADAQABAAABAQD3F6tyPEFEzV0LX3X8BsXdMsQz1x2cEikKDEY0aIj41qgxMCP/iteneqXSIFZBp5vizPvaoIR3Um9xK7PGoW8giupGn+EPuxIA4cDM4vzOqOkiMPhz5XK0whEjkVzTo4+S0puvDZuwIsdiW9mxhJc7tgBNL0cYlWSYVkz4G/fslNfRPW5mYAM49f4fhtxPb5ok4Q2Lg9dPKVHO/Bgeu5woMc7RY0p1ej6D4CKFE6lymSDJpW0YHX/wqE9+cfEauh7xZcG0q9t2ta6F6fmX0agvpFyZo8aFbXeUBr7osSCJNgvavWbM/06niWrOvYX2xwWdhXmXSrbX8ZbabVohBK41 phodgson@thoughtworks.com"
+}
+
+resource "aws_iam_policy_attachment" "test-attach" {
+    name = "test-attachment"
+    roles = ["${aws_iam_role.test-role.name}"]
+    policy_arn = "arn:aws:iam::aws:policy/service-role/AmazonEC2SpotFleetRole"
+}
+
+resource "aws_iam_role" "test-role" {
+    name = "test-role"
+    assume_role_policy = <<EOF
+{
+  "Version": "2012-10-17",
+  "Statement": [
+    {
+      "Sid": "",
+      "Effect": "Allow",
+      "Principal": {
+        "Service": "spotfleet.amazonaws.com"
+      },
+      "Action": "sts:AssumeRole"
+    }
+  ]
+}
+EOF
+}
+
+resource "aws_spot_fleet_request" "foo" {
+    iam_fleet_role = "${aws_iam_role.test-role.arn}"
+    spot_price = "0.005"
+    target_capacity = 2
+    valid_until = "2019-11-04T20:44:20Z"
+    launch_specification {
+        instance_type = "m1.small"
+        ami = "ami-d06a90b0"
+        key_name = "${aws_key_pair.debugging.key_name}"
+    }
+    depends_on = ["aws_iam_policy_attachment.test-attach"]
+}
+`
+
 const testAccAWSSpotFleetRequestWithAdvancedLaunchSpecConfig = `
 resource "aws_key_pair" "debugging" {
 	key_name = "tmp-key"