(MAINT) travis failing on ruby 1.8

 - https://github.com/travis-ci/travis-ci/issues/2217
   Ruby 1.8.7 installs ree-1.8.7-2012.02 instead of MRI
Merge pull request #233 from anodelman/fix-travis

(MAINT) travis failing on ruby 1.8
(QENG-275) redesign beaker's env var support

- move all env vars reading to options parsing
- rename beaker env vars to match format BEAKER_*name*, still support
  old name format for now