aws: store and read instance state

This allows us to store the instance state into the state file. This
means we can now easily see the instance state with `terraform show`.

builtin/providers/aws/resource_aws_instance.go

@@ -132,6 +132,11 @@ func resourceAwsInstance() *schema.Resource {
 				Computed: true,
 			},
 
+			"instance_state": &schema.Schema{
+				Type:     schema.TypeString,
+				Computed: true,
+			},
+
 			"private_dns": &schema.Schema{
 				Type:     schema.TypeString,
 				Computed: true,
@@ -449,12 +454,16 @@ func resourceAwsInstanceRead(d *schema.ResourceData, meta interface{}) error {
 
 	instance := resp.Reservations[0].Instances[0]
 
+	if instance.State != nil {
 		// If the instance is terminated, then it is gone
 		if *instance.State.Name == "terminated" {
 			d.SetId("")
 			return nil
 		}
 
+		d.Set("instance_state", instance.State.Name)
+	}
+
 	if instance.Placement != nil {
 		d.Set("availability_zone", instance.Placement.AvailabilityZone)
 	}