webadmin: clean properties when changing the cluster policy

When user changes cluster policy to 'None' policy the properties
from the previous policy were still visible.

Change-Id: Icb1da2c3d97c63ce6b73cfb3fd68ee7fb05e8ebb
Bug-Url: https://bugzilla.redhat.com/1062234
Signed-off-by: Jiri Moskovcak <jmoskovc@redhat.com>