Dockerised `autoland transplant` for demo/dev of lando/conduit.

Requires a running mercurial server to clone from (at startup) and land to.
Set the REPO_URL environmental variable accordingly.

Requires a postgres database.
Set the DATABASE_* environmental variables accordingly.
Use the `init` command to initialise the database.

Requires running a treestatus.
Set the TREESTATUS_URL environment variable accordingly.

The following environmental variables can be passed into a container to
configure autoland-transplant:

postgres database:
    DATABASE_HOST - hostname (default: autolanddb)
    DATABASE_NAME - db name  (default: autoland)
    DATABASE_USER - username (default: autoland)
    DATABASE_PASS - password (default: autoland)

authentication
    AUTOLAND_KEY - secret key for `autoland` user, used to authenticate landing
                   requests (default: autoland)

repositories
    REPO_URL  - url to the repo for cloning (default: http://autolandhg:8000/)
    REPO_NAME - name of the repo to land to (default: test-repo)

treestatus
    TREESTATUS_URL - format string url to treestatus, usually something of
                     the form "https://<domain>/%s" (default: treestatus/%s)

lando
    LANDO_HOST       - hostname of lando, used to validate pingback urls
                       (default: lando.example.com)
    LANDO_API_KEY    - pingbackup api-key (default: secret)
    LANDO_BUCKET     - s3 bucket holding patches to land (default: lando-dev)
    LANDO_AWS_KEY    - aws key for lando's s3 bucket (default: key)
    LANDO_AWS_SECRET - aws secret for lando's s3 bucket (default: secret)