Start Running tests on Stable JRuby

Fixes for LOT of bugs have now landed in Jruby 1.7.6, thus we no longer
need to run tests against the master.

for broken tests that are still remaning:
1. If problem is in rails - we fix that test/code
2. if its a JRuby bug - we skip that test & file a bug report for jruby.
Merge pull request #12814 from gaurish/enable-jruby19-again

Start Running tests on Stable JRuby