add iam_role_policy_attachment resource

[nakamasato]

Why

• There's iam_policy_attachment but it's exclusive and there's a risk to accidentally revoke an attachment that is managed outside of this resource. For more details, please refer to the warning on the official documentation. https://www.terraform.io/docs/providers/aws/r/iam_policy_attachment.html

What

• Use iam_role_policy_attachment, iam_group_policy_attachment or iam_user_policy_attachment as the documentation suggests.
• Only iam_role_policy_attachment is added in this PR

Check

• Added resource: iam_role_policy_attachment

• Class name: IAMRolePolicyAttachment

• File name: iam_role_policy_attachment.rb

• Command name: iamrpa

• Executed terraform plan for my own resources and confirmed there's no changes

  terraform plan
  
  ...
  
  ------------------------------------------------------------------------
  
  No changes. Infrastructure is up-to-date.
  
  This means that Terraform did not detect any differences between your
  configuration and real physical resources that exist. As a result, no
  actions need to be performed.
  

Future work

Add iam_user_policy_attachment and iam_group_policy_attachment

[coveralls]

Coverage remained the same at 100.0% when pulling 3269925 on nakamasato:iam_role_policy_attachment into 518879d on dtan4:master.

[coveralls]

Coverage remained the same at 100.0% when pulling 4dc2401 on nakamasato:iam_role_policy_attachment into 518879d on dtan4:master.