which will build a "dirty" image using the working directory.
This command is different from `build push` in two important ways:
- the image tags will have a suffix of `-dirty`
- the export action is "docker", pushing to the local docker image store
The command also supports the `--output` option just added to `build
push` to override that default.
This command is intended to allow developers to quickly iterate on a
docker image built from their local working directory while avoiding
any confusion with a pristine image built from a git clone, and
keeping those images on the local dev system by default.