Sync the OSX CI eagerly and add diagnostics.

Move the OSX CI sync up-front to leverage parallelism
instead of waiting on the whole local build matrix to complete.

Also add diagnostics that record why the sync is skipped if
skipped in addition to making skipping & syncing decisions more
robust and explicit.

Testing Done:
CI away here already shows proper fork sync-skipping diagnostic: https://travis-ci.org/pantsbuild/pants/builds/35967008
This will have to land on pantsbuild/pants master to vet fully.

Bugs closed: 599

Reviewed at https://rbcommons.com/s/twitter/r/1064/
Fixup ci-sync.sh to cover committer ident.

Testing Done:
None - can only be tested on pantsbuild.pants master, but in response to this failure: https://travis-ci.org/pantsbuild/pants/jobs/35969933
CI did go green here though - so nothing horribly more broken: https://travis-ci.org/pantsbuild/pants/builds/35972662

Bugs closed: 600

Reviewed at https://rbcommons.com/s/twitter/r/1065/
Remove recommendation of manual edits to the pushdb

The manual-edits-to-the-pushdb approach gets a bit too down and dirty. Remove the recommendation in favor of resetting and using --publish-override.

Reviewed at https://rbcommons.com/s/twitter/r/1056/
Merge branch 'master' into areitz/add_publish_plugins
add a negative test
more cleanups