Remove support for binding ports on VLAN networks

OVSDB in ODL doesn't support VLAN networks yet, so remove this support from
the MechanismDriver binding code for now. We'll add this back if we ever
support VLANs in OVSDB+ODL.
Merge branch 'odl_ml2' of github.com:CiscoSystems/neutron into odl_ml2