BentoML

It would be nice if there was a command like:

`bentoml containerize myservice:latest --tag new_name_for_myservice:new_tag`

where it would containerize myservice:latest, but it would now have the new_name_for_myservice:new_tag as the docker tag.

Hey Dimitri, this is already available as of now.
```Options:
  -t, --image-tag, --docker-image-tag NAME:TAG
                                  Name and optionally a tag (format: ``name:tag``) for building container, defaults to the bento tag.```
You can type `bentoml containerize --help` to see them!