webadmin: fix volume bricks tab refresh issue

Bricks sub-tab was not showing the data  immediately
when the user is navigating in the volume sub-tabs.
This is now fixed.

Refactored remove-brick actions availablity and
avoided setting the entity directly from VolumeListModel.

Change-Id: If91de652fe7e88df063a871948c0abbda7647698
Bug-Url: https://bugzilla.redhat.com/1012871
Signed-off-by: Kanagaraj M <kmayilsa@redhat.com>