NXCM-5194: G level MD deploy

As turns out, those are locally staged, but not remotely
deployed into staging repo (or to hosted repo in case of
deferred deploy, both are affected).

Reason was that "remote deploy" is driven by an "index file"
that simply enlists all the artifacts deployed, but NOT
metadata. This is a problem in case of G level MD, as
other MDs are handled transparently by deployer, while
G level MD is not.

This is merely a "quickfix" for the problem, it makes
it work, but has it's own compromises.
Merge remote-tracking branch 'origin/master' into nxcm-5194-g-level-md-deployment
NXCM-5194: Fixed wrong references in POM

Some dependencies got G's change, updated
and staging plugin bumped to latest.
NXCM-5194: WIP/ IT

This is WIP, not done yet
NXCM-5194: plugin G was changed
NXCM-5194: IT POMs updated to support java6 level

As annotations are used on Mojos
NXCM-5194: Making plugin prefix unique

As otherwise, the 3 runs in IT would produce illegal
3 deploys with same plugin prefix and different
artifact IDs
NXCM-5194: Exposing NexusClient

To allow ITs access to other needed subsystems
NXCM-5194: ITs

Two ITs introduced, one exercising "Deferred deploy" while
other the "staging".

Both are checking for presence and validity of the deployed
G level repository metadata by fetching and parsing it's content
and asserting expected entries.
NXCM-5194: Getting rid of Java7 signatures
NXCM-5194: Moving method level up

Initially I thought I'll need "release" to be run
in the staging scenario but I realized this is not
the case. Closed staging repo is just fine as everything
else
Merge remote-tracking branch 'origin/master' into nxcm-5194-g-level-md-deployment

Conflicts:
	m2settings/pom.xml
	staging/pom.xml
NXCM-5194: The list might not contain nulls

Also, the Function is not expecting nulls either.
Fix for null case
Merge pull request #34 from sonatype/nxcm-5194-g-level-md-deployment

NXCM-5194: G level MD deploy