Provides ability to reference existing neutron resources

Additional properties 'network' and 'subnet' are added to
the resources (existing properties 'network_id' and
'subnet_id' are deprecated). 'network'  and 'subnet' can
now carry name or id. Pre-existing neutron resources
can now be referenced in heat templates by their name
and not necessarily by their UUID. This would help porting
templates across deployments.

Change-Id: I644f5d6ee2e5ccabde190bd73eacc71daaf41f4d
Closes-Bug: #1286128
Merge "Provides ability to reference existing neutron resources"