initial ml2-gre implem

Change-Id: I1b32c1c28d0e714921e6660860723b17d7be6fa8
add support for GRE
add gre id allocation in table when type_gre initialize

Change-Id: I5f70b335224bf57c2db6834cd8c5f71f73d23957
rpc tunnel_update consumer created + bug fix
add provider network mgt to type_gre

Change-Id: I275126d953c7165f4132fc69f4e40a3444174b59
Merge branch 'bp/ml2-gre' of https://github.com/mathieu-rohon/quantum into bp/ml2-gre

Conflicts:
	etc/quantum/plugins/ml2/ml2_conf.ini
remove default value for type_driver