webadmin: Store rest api session id in http session

- REST API stores a session id for the UI plugins.
  Moved the session id location from LocalStorage to
  HTTP session.

Change-Id: I6fe9af54054aefe694876b1805a4a44f9bba0482
Bug-Url: https://bugzilla.redhat.com/show_bug.cgi?id=1077448
Signed-off-by: Alexander Wels <awels@redhat.com>