Fixed broken beet-random-playback-loop.py.
Previous commit didn't quite work right.
Modified beet-random-playback-loop.py, silencing all output.
Unlike with mplayer, sending mpv's stdout to /dev/null somehow breaks
stdin, making it impossible to move forward or backward during
playback.  I removed the redirect and added the "--really-quiet"
option to the command line.  Unfortunately, this eliminates all
output, including the status line (which is all I care about).