We have lots of issues out there where people get easily confused by mbs-build local.

• It is unclear that the yaml file has to be in cwd, and that it has to have the same name as the directory.
• It is unclear that it has to be committed to git.

@thozza has made the point that it is unreasonable to expect developers to commit their yaml files before they can even do a local test build.

We should fix this. Let's allow mbs-build local to accept a bare yaml file, either on disk or at some url.

• In this case, MBS cannot guess the stream name, since it is derived from the git branch. mbs-build local should grow a --stream option to allow the user to specify it.
• MBS also cannot guess the version of the module, since it is derived from the git commit timestamp. The current time pulled from datetime.datetime.utcnow() should be used instead.