Allow an in-progress stack to be deleted

Since multi-engine was merged, it is no longer possible to delete a
stack which is create/update IN_PROGRESS.  This re-introduces that
ability.

If the current engine has an active stack lock, stop any active
threads, remove the lock, and delete the stack.  If another engine has
the active stack lock, send an RPC command to the remote engine to stop
any active threads and remove the lock, and then delete the stack
locally.  If no engines have the an active stack lock, acquire the lock
and delete the stack.

Closes-Bug: #1262012
Change-Id: I188e43ad88b98da7d1a08269189aaefa57c36df2
Merge "Allow an in-progress stack to be deleted"