CLOUDSTACK-5967: GRE tunnel creation is failing

after network orchestrator refactor, only network elements providingg
services as defined by network offering, are invloved network design and
imlement phase. So OVS network element need to be enables as
'Connectivity' service provider to make GRE tunnels work. This fix
introduced 'Ovs' provider as Connectivity service provider.

Conflicts:
	server/src/com/cloud/network/NetworkServiceImpl.java