[travis] get travis back to happy (#1022)
- Set minimum maven version to 3.1.0+, due to reqs for ES testing
- remove oracle jdk7 per travis-ci/travis-ci#7884
- Skip ES5 cluster spin-up if tests are skipped.
- Increase test heap for asynchbase binding from Travis 2048m to 4096m
- temporarily remove the riak service on travis
- currently fails w/o details
- http://docs.basho.com/ fails to load, so I can't spin up a test node locally.