provider/aws: Deprecate roles in favour of role in iam_instance_profile (#13130)
provider/aws: Deprecate roles in favour of role in iam_instance_profile (#13130)

* provider/aws: Deprecate roles in favour of role in iam_instance_profile

You can only specify a single role to an IAM Instance Profile. So having
a slice of roles in the provider makes no sense. Therefore, we are going
to deprecate this infavour of `role`

```
% make testacc TEST=./builtin/providers/aws TESTARGS='-run=TestAccAWSIAMInstanceProfile_'
==> Checking that code complies with gofmt requirements...
go generate $(go list ./... | grep -v /terraform/vendor/)
2017/03/28 21:24:20 Generated command/internal_plugin_list.go
TF_ACC=1 go test ./builtin/providers/aws -v -run=TestAccAWSIAMInstanceProfile_ -timeout 120m
=== RUN   TestAccAWSIAMInstanceProfile_importBasic
--- PASS: TestAccAWSIAMInstanceProfile_importBasic (25.08s)
=== RUN   TestAccAWSIAMInstanceProfile_basic
--- PASS: TestAccAWSIAMInstanceProfile_basic (22.40s)
=== RUN   TestAccAWSIAMInstanceProfile_withRoleNotRoles
--- PASS: TestAccAWSIAMInstanceProfile_withRoleNotRoles (22.63s)
=== RUN   TestAccAWSIAMInstanceProfile_missingRoleThrowsError
--- PASS: TestAccAWSIAMInstanceProfile_missingRoleThrowsError (4.02s)
=== RUN   TestAccAWSIAMInstanceProfile_namePrefix
--- PASS: TestAccAWSIAMInstanceProfile_namePrefix (22.18s)
PASS
ok  	github.com/hashicorp/terraform/builtin/providers/aws	96.349s
```

* Update iam_instance_profile.html.markdown

kjmkznr/terraform-provider-aws,ClementCunin/terraform-provider-aws,ashinohara/terraform-provider-aws,ashinohara/terraform-provider-aws,Ninir/terraform-provider-aws,nbaztec/terraform-provider-aws,ashinohara/terraform-provider-aws,ClementCunin/terraform-provider-aws,charles-at-geospock/terraform-provider-aws,Ninir/terraform-provider-aws,kjmkznr/terraform-provider-aws,charles-at-geospock/terraform-provider-aws,ashinohara/terraform-provider-aws,nbaztec/terraform-provider-aws,charles-at-geospock/terraform-provider-aws,kjmkznr/terraform-provider-aws,nbaztec/terraform-provider-aws,ClementCunin/terraform-provider-aws,terraform-providers/terraform-provider-aws,kjmkznr/terraform-provider-aws,Ninir/terraform-provider-aws,terraform-providers/terraform-provider-aws,Ninir/terraform-provider-aws,ClementCunin/terraform-provider-aws,charles-at-geospock/terraform-provider-aws,nbaztec/terraform-provider-aws,terraform-providers/terraform-provider-aws,terraform-providers/terraform-provider-aws