Add role_arn to delete function in stack.py

[jtanton]

Overview

Update stack.py delete function to use an optional role_arn parameter during delete stack.

Testing/Steps taken to ensure quality

Peer reviewed but needs additional testing to validate.

Notes

Optional. Caveats, Alternatives, Other relevant information.

Testing Instructions

How to test this PR Start after checking out this branch (bulleted) Use role_name in project to create a stack and confirm the delete is also done by the same role.

[jtanton]

Turns out the caller identity performs the delete stack and not the the cloudformation service so this change isn't needed.