Make travis run etcd integration tests

[mwitkow]

Currently SBT runs Junit integration tests with --exclude-categories=org.flagz.IntegrationTestCategory by default.

That's to make sure that integration tests are easy to consume by contributors (not needing etcd running) Figure out a way to pass that Junit runner parameter to sbt test so that it can be set in .travis.yml.

Add a before_script similar to https://github.com/skynetservices/skydns/blob/master/.travis.yml to download a set release of etcd and test against that.