Changed logging to use glog library.

Also fixed versioning and added check for test image existence when running integration tests.
What I'd like to see still, is the possibility to redirect docker stderr & stdout to logger, as well as forcing glog to spit everything to stdout and not stderr as it is right now.

@csrwng @bparees comments welcome.
if `env` is nil then `env.Value.String()` panic imho