NX-126: migrate use of Plexus component descriptor API to Sisu API
NEXUS-6242: Reveal the real cause too,
NEXUS-6232: Prevent concurrent execution of createrepo on same data

Added exclusive lock around MD generation (invocation of createrepo)
that assures that on same repository instance only one
Generate Yum Metadata task will run, while the others will remain
blocked waiting for the lock.
Merge pull request #328 from sonatype/NX-126-more-plexus-cleanup

REVIEW: migrate use of Plexus component descriptor API to Sisu API
Fixing since tags.

Some of them were backported.
Some of them originates from security 2.8, when
the project was on it's own repository. Using
already used designation for those, prepending
project name to version to avoid clash.

Note: Security was at version 2.8 when it got
squashed into Nexus OSS repository. Today,
Nexus is at version 2.8, but we had leftovers
of some security components having no designation
and hence, leading to confusion.
NEXUS-6220: Adjust since tags
Merge remote-tracking branch 'origin/master' into NEXUS-6232-concurrent-createrepo
NEXUS-6232: Adjust mocks in UTs

As created mocks lacked some responses.
NEXUS-6232: Adjusting mocks
Merge pull request #334 from sonatype/NEXUS-6232-concurrent-createrepo

NEXUS-6232: Prevent concurrent execution of createrepo on same data
NEXUS-6258: AR interferes with NFC

As request context is reused, the request rejected from
AR will disable NFC for all subsequent proxy participants.
Merge pull request #340 from sonatype/NEXUS-6258-AR-kills-nfc

NEXUS-6258: AR interferes with NFC
Merge remote-tracking branch 'origin/master' into upgrade-hc4