Ensure auth_endpoint is reset

The auth_endpoint variable is loaded from glance-api.conf, thus it
should be cleared when configurations loaded by glance-api.conf is
cleared.

Change-Id: I77fddcb26589dd975043c2487e672c26013479fc

lib/puppet/provider/glance.rb

@@ -92,6 +92,7 @@ class Puppet::Provider::Glance < Puppet::Provider::Openstack
   def self.reset
     @glance_conf = nil
     @glance_credentials = nil
+    @auth_endpoint = nil
   end
 
   # To keep backward compatibility