rsync: Remove hardcoded --quiet option.

rsync: Remove hardcoded --quiet option.

When running in daemon mode, the stdout and stderr stream of dss and
all its child processes are redirected to /dev/null. In particular any
output from the rsync process is discarded. Therefore, whenever a new
snapshot is created, dss currently passes --quiet to the underlying
rsync command, along with --archive and --delete.

However, as was pointed out by Sebastian Schultheiß, if the rsync
command fails for unknown reasons, the --quiet option complicates
debugging for the questionable benefit of saving the I/O for a few
writes to /dev/null.

This patch removes the --quiet option.