webadmin: Only add VNIC if profiles available

Changed the logic slightly to only create a default VNIC for a new VM
if there are profiles to choose from. Otherwise, the automatic
addition of an empty VNIC might lead to inability to create a VM in a
3.1 cluster, if there's no profile available.

Change-Id: I8b582711252be833300a8819c86159dd9058c1e9
Signed-off-by: Lior Vernia <lvernia@redhat.com>