Don't delete stack domain project on stack-abandon

Currently we delete the stack domain project on abandon, which will
break any resources being abandoned that depend on users created in
the stack user domain.  So add a flag to skip deletion on abandon
and some tests to prove it works.

Change-Id: I883831a33d5bd326523836247683c161f797ee2a
Closes-Bug: #1300734
Merge "Don't delete stack domain project on stack-abandon"