Switched to using gid rather than groups

The gid is for the primary group, which is what we want to specify here.
Added ability to mount report volume

This update will mount and unmount report_vol, as well as adding or
removing the mount point depending on the service status, in order to
place the source of truth inside puppet rather than having it somewhere
else. If you don't want the module to handle mounting, you can leave the
fstab_entry as undef.