Sub-commands: run, fetch #6
Description
Many python utilities and programs such as git provide several sub-commands with specific-arguments. E.g. git-clone has a man page but isn't an actual executable. It's just a sub-commands of git with sub-command-specific options.
We should do the same for pipeline-commander. Namely, add a "run-pipeline" command, which would encapsulate the current functionality, and also add a "fetch-artifact" command which would allow the user to fetch one or more named artifacts from a given build.