Disables OVS Tunneling When Using VLAN Networking

Previously, OVS tunneling would be enabled when using the
Quantum OVS VLAN networking mode.  OVS Tunneling should not be
enabled when using the VLAN networking mode.

Since ovs_enable_tunneling was not exposed upstream in the
openstack::compute class, this change relies on the following patch:

https://review.openstack.org/#/c/40146/

Reference VLAN Installation:

http://docs.openstack.org/trunk/openstack-network/admin/content/demo_installions.html