webadmin : Allow deletion of sub-volumes from distributed-replicate volume

Refactored the code to allow, deleting multiple
sub-volumes from distributed-replicate volume.

Change-Id: Ib02785bc87af782a3d51c784bedac4e3d0e1b15a
Bug-Url: https://bugzilla.redhat.com/show_bug.cgi?id=1031585
Signed-off-by: Anmol Babu <anbabu@redhat.com>
Signed-off-by: Kanagaraj M <kmayilsa@redhat.com>