Privilege checking for heat-keystone-setup-domain

This patch added additional exception handling so that a non-admin user
will understand why his/her attempt to run this script failed.

Change-Id: I20a593f613931de0b3c13094a2e0b6c2f2b0eea1
Closes-Bug: 1354687
Merge "Privilege checking for heat-keystone-setup-domain"