webadmin: save search query

- Use the current search query when switching to a main tab from
  another main tab. Before it would use the default search query
  instead of the current used one. When selecting items in the
  system tree it will reset the current query to the default.

Change-Id: I9f72f406e467ba90ad6800429492427c3f14a6a3
Bug-Url: https://bugzilla.redhat.com/show_bug.cgi?id=1172389
Signed-off-by: Alexander Wels <awels@redhat.com>