Add hint on creating new user for Heat in DevStack

Mention heat_stack_owner role in the docs for DevStack.

Change-Id: I5f3e0405684fffa0aa05d1552ca0f6e7074471aa
Partial-Bug: #1306665
Implement locking in abandon stack

This change implements locking in abandon stack. If lock
acquire fails throws ActionInPrgoress exception.

Change-Id: I930123efa95b2863c4e2de01f4646b6e3d68c5cc
Closes-bug: #1301311
Merge "Implement locking in abandon stack"
Merge "Add hint on creating new user for Heat in DevStack"