PLUMgrid plugin v2

This commit implements blueprint plumgrid-plugin-v2

Includes PLUMlib Library
Fake PLUMLib library for Unit Tests
Remove the use of topologies
Includes IOVISOR VIF driver
Implements External Networks

Change-Id: I8ba90862e5a416d04d3327b46fcb0f6f3fa65248
Merge "PLUMgrid plugin v2"