Dockerize oplog-replay as worker

This change adds a dockerfile to run oplog-replay as a worker. It does
this by using the baseworker-go/taskwrapper code. This listens to
Gearman for requests to process the job.

This change also publishes the docker image to docker hub
I'm not sure how oplogdump / oplogreplay depend on one another - but just ensuring that this --cmd should point to oplogdump and not oplog replay?