webadmin: fix tabs shown/hidden when tags selected/unselected

Fixed tab show logic so that when a tag is selected, only Hosts, VMs, and Users
tabs are visible. When no tag is selected, tabs behave as if System node is
selected.

Change-Id: I6cace6daecef58ee2726a22e880d5c31e03e275f
Bug-Url: https://bugzilla.redhat.com/1006282
Bug-Url: https://bugzilla.redhat.com/996594
Signed-off-by: Greg Sheremeta <gshereme@redhat.com>