exit cleanup in functions

we should always use die instead of exit so that we know why we
failed.

Also remove instances where exit is called after die, as that is
a noop.

Change-Id: I8e08cce63d35c503c36ff1e09805f3db427d082d
final bash8 files for the rest of devstack

With this devstack/master is bash8 clean, and ready for enforcement

Change-Id: I03fc89b401e6b7a23224d71472122c1bfa3ad0bd
Merge "exit cleanup in functions"