Implements provider network support in PLUMgrid plugin

Includes the provider network extension in PLUMgrid plugin
PLUMgrid drivers are updated with the new extension data
Unit tests are added

Change-Id: Ia7fc011c04d143bdb7fd8f67768a2076be8c5264
Implements: blueprint provider-network-plumgrid
DB Mappings for NSX security groups

This patch introduces DB mappings between neutron security
groups and NSX security profiles, thus not requiring anymore
the Neutron router ID to be equal to the NSX one.

This change is needed for enabling asynchronous operations in
the NSX plugin.

Related to blueprint nvp-async-backend-communication

Change-Id: I3b28d535c93cd2bfc776aabe0d99be18fce4454d
Merge "Implements provider network support in PLUMgrid plugin"