webadmin: Cluster policy details moved to a new sub-tab

Cluster policy details are moved from cluster's 'General' sub-tab
to a new 'Policy' sub-tab. Policy sub-tab will be shown only if
the selected cluster supports virt service.

Refactored ClusterPolicyModel code.

'Cluster Node Type' field in General tab will be visible
only if the application is running on Virt+Gluster mode.

Change-Id: I600b1614f6e8a1a82b254b76c7713678cfb9e557
Bug-Url: https://bugzilla.redhat.com/920078
Signed-off-by: Kanagaraj M <kmayilsa@redhat.com>