minimega: allow "minimega" group to execute commands

[ccordi]

We would like users to be able to run minimega commands without needing to be root. Instead, it would be preferable if all users that are part of the "minimega" group could execute commands.

This functionality could be achieved by running something similar to the following after starting minimega:

  chgrp -R minimega $MM_RUN_PATH
  chmod -R g=u $MM_RUN_PATH
  chmod g+s $MM_RUN_PATH ${MM_RUN_PATH}/minimega

This could likely be done in the systemctl script or by minimega on startup.