Fix aws_iam_policies unit tests

[rmoles]

It appears the unit test(s) for aws_iam_policies are currently broken. When running the unit tests the following errors occur:

AwsIamPoliciesTest#test_policy_attached_users [/Users/rmoles/git_repos/inspec-aws/test/unit/resources/aws_iam_policies_test.rb:60]:
Expected: ["test-user"]
  Actual: [{:user_name=>"test-user"}]

AwsIamPoliciesTest#test_policy_attached_roles [/Users/rmoles/git_repos/inspec-aws/test/unit/resources/aws_iam_policies_test.rb:56]:
Expected: ["test-role"]
  Actual: [{:role_name=>"test-role"}]

[quietarcade]

Issue is invalid.