backend: Lessen permissions needed for VmPool creation

Changed AddVmPoolWithVmsCommand to require only CREATE_VM permission
for the template instead of CREATE_VM_POOL to make it consistent with
user's ability to create VMs.

Change-Id: Ib28ae681a91d7b11455283041062779733e61f2b
Bug-Url: https://bugzilla.redhat.com/show_bug.cgi?id=1058290
Signed-off-by: Martin Betak <mbetak@redhat.com>