webadmin: VM dialog - organize resource allocation section

VM dialog -> Resource Allocation:
To improve tab display, added 'Disks Allocation'
section which contains disks related widgets:
- Disks table.
- VirtIO-SCSI checkbox.

Screenshot: http://i.imgur.com/J5TypMQ.jpg

Change-Id: Ic16354dcfc7cc50a8e1969b54e0ca32722e54e8f
Signed-off-by: Daniel Erez <derez@redhat.com>