How should plugins tell what type of pioreactor they should be installed on?

[CamDavidsonPilon]

Some plugins might only work on the leader, or worker on leaders and workers. Not all plugins make sense to work on leader. How should plugins tell us?

[CamDavidsonPilon]

Options:

• A flag-file in the .whl. This option is okay, it requires us to download the wheel file, unzip it, and look inside, then install the whl (possibly). But the install will no-op.

• a no-op in the __init__. Ex:

  from pioreactor.whoami import am_I_leader
  
  if am_I_leader():
    from .... import ....

  I'm not even sure this would work, but it's flexible. Another problem is that it will still install the library, so it would show up in pio list-plugins. This doesn't really work with files with code in the __init__.py