Minor changes/bug fixes:

• Kill any stale RDS instances that might still be running
• Log the RDS binary output if in debug mode
• Don't background rds in a subshell to make this block properly for FPP
  playback.  Without removing the backgrounding in a subshell we'd
  return and the song would start playing while we were talking to the
  vast over USB, creating some static during the beginning of the song.