webadmin: System permissions tab don't update

System permissions tab doesnt update content on
initialization and after a new user is added and
displays the cached content until the refresh is
called in afew seconds.

This patch calls the refresh on the model each time
a user is added or when the ConfigurePopupPresenterWidget
is revealed.

Change-Id: I04cb331ec9a1ac0868265353bcc387a202225821
Bug-Url: https://bugzilla.redhat.com/show_bug.cgi?id=861964
Signed-off-by: Ravi Nori <rnori@redhat.com>