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
Merge "Implements provider network support in PLUMgrid plugin"