To switch to a local battle-hardened Docker Machine VM:
eval $(docker-machine env) # in every running shell
And, optionally, stop the Docker Beta via the whale icon on the menubar.
To switch back to the beta, start it if you stopped it before, and run
eval $(docker-machine env -u) # in every running shell
The other more direct answer is that the Docker beta is set up to work if all of the
DOCKER_* environment variables, and most importantly
DOCKER_HOST, are unset.