webadmin: Allow selection of None for Cloud-Init network boot protocol

The REST API supported DHCP, Static IP, and None as NIC address types
for cloud-init VM startup.  Make the same available in the UI as well.

Change-Id: Ic51a76e968922fb62a07ccaced969c8b580de083
Bug-Url: https://bugzilla.redhat.com/1120092
Signed-off-by: Greg Padgett <gpadgett@redhat.com>
Signed-off-by: Moti Asayag <masayag@redhat.com>