$ IMAGE=mygroup/myimage:mytag
$ OLDREG=test-registry.company.com
$ NEWREG=stage-registry.company.com
$ docker pull $OLDREG/$MYIMAGE
[...]
$ docker tag -f $OLDREG/$MYIMAGE $NEWREG/$MYIMAGE
$ docker push $NEWREG/$MYIMAGE
$ docker rmi $OLDREG/$MYIMAGE
$ docker rmi $(docker images -q --filter dangling=true)
