core: fail when trying to remove labeled VLAN network.

Vlan related nics cannot have labels, but when I have VLAN enabled non
vm network added to nic via label, then this nic will have associated
label, and vlan related nic will have associated network. So  I have to remove
Vlan related nic when updating via setupnetworks, to remove network.

So I have to check base interface for label presence when removing
network with vlan enabled via removing of vlan related nic.

Also it seemed to me like a bug, that if isVlan(nic) is true, but it's
base interface nic is present in setupnetworks request(ie. vlan
related nic was deleted but base interface was not), vlan related
nic is checked for label presence, although it's base resource should
have been validated.

Change-Id: I132f4ae124e45144beee21f81f69e55ed25cd540
Bug-Url: https://bugzilla.redhat.com/1134380
Signed-off-by: Martin Mucha <mmucha@redhat.com>