Check if auth_admin_prefix is defined
Check if auth_admin_prefix is defined

Check if auth_admin_prefix is defined (passed as a parameter to api.pp)
before trying to access it in the settings data structure.

Change-Id: I61a3ae41dca2a5e5bd9e635b0a2ab9eb05b0326a
Fixes: bug #1190481

varunarya10/puppet-glance,varunarya10/puppet-glance,aquto/puppet-glance,mjeanson/puppet-glance,mjeanson/puppet-glance,TelekomCloud/puppet-glance,gwdg/puppet-glance,TelekomCloud/puppet-glance,aquto/puppet-glance,gwdg/puppet-glance