webadmin: hide VM sub-tab when selecting a gluster cluster

'Virtual Machines' sub-tab of Cluster will be shown only
if the user selects a cluster which supports virt.

Change-Id: I4057c7221510dc72bb7dd582ca6b2c9a42b01404
Bug-Url: https://bugzilla.redhat.com/920106
Signed-off-by: Kanagaraj M <kmayilsa@redhat.com>