Stop creating KeystoneAdmin KeystoneServiceAdmin sysadmin netadmin roles

These roles have absolutely no use anymore since quite some time. And
they were dropped from the sample data in Grizzly:
https://github.com/openstack/keystone/commit/d6f7cbc484868bdec3eeb9d4b0f45b10ce536e79
Merge pull request #90 from vuntz/drop-unneeded-roles

Stop creating KeystoneAdmin KeystoneServiceAdmin sysadmin netadmin roles