* 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
  - https://docs.travis-ci.com/user/build-environment-updates/2017-09-06/
* 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.

This commit sets the Elasticsearch 5 binding to only use the
elasticsearch-maven-plugin if tests are running on JDK 8.

This commit fixes issues with the Elasticsearch 5 transport client and
REST client bindings so that all tests pass.

This commit bumps the Elasticsearch dependency version of the
Elasticsearch 5 binding to version 5.5.1.