Add ability to manage Neutron ML2 plugin package state

Introduce the package_ensure parameter to add the ability
to manage Neutron ML2 plugin package state.

Conflicts:
  manifests/plugins/ml2.pp

Closes-bug: #1355370
Change-Id: I3bf6ed68015c13cf61db1b43dfbf4fd3c845d00f
(cherry picked from commit 7d20fc90ed75fbb6fd61a92254e5b0ca32475b31)
Merge "Add ability to manage Neutron ML2 plugin package state" into stable/icehouse