Retry rabbitmq password change

Due to the bug referenced below, on Fedora it is possible for
the rabbitmq password change to fail the first time rabbitmq is
started.  This change adds a retry loop to avoid the problem in
devstack.  One retry should be enough in most (all?) cases, but
this will retry up to ten times just to be safe.

Note that just retrying the password change is not enough.  The
rabbitmq-server service must be restarted as well.

Change-Id: I403dcd503aa8e74e2ba6312a0decf0d4fd0d8795
bz: https://bugzilla.redhat.com/show_bug.cgi?id=1059028
Merge "Retry rabbitmq password change"