webadmin: Add FencingPolicy to cluster configuration

Adds Fencing Policy tab to cluster detail.
Adds option to skip fencing of host if it's connected to at least one
storage domain to Fencing Policy tab.

Change-Id: Iaecc1662324ce3d3072c9e850fcf8026ccfab0b2
Bug-Url: https://bugzilla.redhat.com/1090799
Signed-off-by: Martin Perina <mperina@redhat.com>