webadmin: Optimize for virt store while creating volume

'Optimize for Virt Store' checkbox is added to the
Create Volume dialog.

Change-Id: I98e2e636a67e0b7f204e45a3e3d39bdec96eeeb0
Bug-Url: https://bugzilla.redhat.com/891493
Signed-off-by: Kanagaraj M <kmayilsa@redhat.com>