Fix case of OVS group in ovs_quantum_plugin.ini.

Fixes bug 1185976

Quantum switched to a lower case group name but it didn't
last long, see https://review.openstack.org/#/c/30794/

Change-Id: I771b895ca795e5e3427b22e6bedbc4ec51cc0394
Merge "Fix case of OVS group in ovs_quantum_plugin.ini."