Fixes 2 acceptance tests for the `aws_instance` data source
```
$ make testacc TEST=./builtin/providers/aws TESTARGS='-run=TestAccAWSInstanceDataSource_SecurityGroups'
==> Checking that code complies with gofmt requirements...
go generate $(go list ./... | grep -v /terraform/vendor/)
2017/01/31 12:12:15 Generated command/internal_plugin_list.go
TF_ACC=1 go test ./builtin/providers/aws -v -run=TestAccAWSInstanceDataSource_SecurityGroups -timeout 120m
=== RUN TestAccAWSInstanceDataSource_SecurityGroups
--- PASS: TestAccAWSInstanceDataSource_SecurityGroups (119.14s)
PASS
ok github.com/hashicorp/terraform/builtin/providers/aws 119.172s
```
```
$ make testacc TEST=./builtin/providers/aws TESTARGS='-run=TestAccAWSInstanceDataSource_tags'
==> Checking that code complies with gofmt requirements...
go generate $(go list ./... | grep -v /terraform/vendor/)
2017/01/31 12:15:42 Generated command/internal_plugin_list.go
TF_ACC=1 go test ./builtin/providers/aws -v -run=TestAccAWSInstanceDataSource_tags -timeout 120m
=== RUN TestAccAWSInstanceDataSource_tags
--- PASS: TestAccAWSInstanceDataSource_tags (118.87s)
PASS
ok github.com/hashicorp/terraform/builtin/providers/aws 118.900s
```