1080609 - pulp-manage-db now ensures the admin.

The webserver used to create the admin role and user if it didn't exist
upon startup. Once Pulp started to be deployed to multiple processes,
this caused a uniqueness constraint to be raised during the first
startup of Apache, as each process raced to create the admin user
simultaneously.

This commit moves the admin role and user creation into the
pulp-manage-db script.

https://bugzilla.redhat.com/show_bug.cgi?id=1080609
Merge branch 'rbarlow-1080609'