Fixes missing docker login when using private registry

[djbelieny]

When using a private docker registry, docker commands in prepare-bundle and meteor-start scripts were not login into the private registry. Updated the code to receive the registry info from the config file and do the actual docker login when privateRegistry is set.

[zodern]

Thanks @djbelieny for submitting this.

Mup should be logging into the registry during mup setup / mup docker setup, and docker should stay logged in. Does this not work for you?

[djbelieny]

Hum... I don't remember doing a mup setup again since it was an app running in production that has been deployed for a long time (over a year), when mup did not suport private registry. We decided to upgrade the mup config and start sending the builds into a private registry to improve deployment times once it became available. The documentation did not mention that we would have to re-setup. Regardless we tried "everything" and it did not seem to login correctly until we modified the files in the PR.

[djbelieny]

Oh. another thing, this is being used to deploy from a pipeline in Bitbucket building and putting the images into a DIgital Ocean container registry. I am not sure, but maybe the docker login happens in the pipeline vm which is volatile and only exists during the CI deployment, being deleted after each deployment.