Optimize jruby cucumber environment

MSP-9895

Get JVM option tuning from 'aruba/jruby' and double timeout to 6 seconds
to fix timeout errors when running `rspec`.
Add timeout doubling for rbx cucumber too

MSP-9895

I can't reproduce the timeout locally with rbx, so I just have to try
the doubling that made JRuby work to see if it fixes rbx on travis-ci.