Added missing core_plugins symbolic names

Some plugins miss short symbolic name in setup.cfg, specifically Nuage
and Metaplugin.

Conflicts:
	setup.cfg

Change-Id: I0198ae98654bbdddf8f2ba8dd3b80d0d447d6341
Closes-Bug: 1324487
(cherry picked from commit 664bdcdc7d714bcdfe503db8f59c6a3f97668df2)
Merge "Added missing core_plugins symbolic names" into stable/icehouse