tests: add .travis.yml for travis-ci integration and allow OMCACHE_AGAIN from stats call

For resolving issue #9 add .travis.yml to run tests automatically using travis. This still needs to be done by signing in to travis and enabling travis for project saaros/omcache (steps 1 and 2: http://docs.travis-ci.com/user/getting-started/). I tried this in my own fork and it seems to work ok: https://travis-ci.org/peekeri/omcache.