PLUMgrid plugin decomposition

PLUMgrid plugin decomposition

As part of the plugin decomposition work, this change
removes PLUMgrid plugin code from Neutron and moves it
to networking-plumgrid repo [1]. Plugin code, config,
drivers and unit test cases are all moved to
networking-plumgrid.

Updated vendor decomposition progress chart

[1] https://github.com/stackforge/networking-plumgrid

Partially-implements: blueprint core-vendor-decomposition
Closes-bug: #1426752
Change-Id: I34c952d1c259f44ed8028ded0b58a5db908dd245