Parsing the mount table with libmount races against the mount command,
which will handle the actual mounting before updating utab. This means
the poll event on /proc/self/mountinfo can kick of a reparse in systemd
before the utab information is available.
This change adds in an additional event source using inotify to watch
for changes to utab. It only watches for IN_MOVED_TO events, matching
libmount behavior of always overwriting this file using rename(2).
This does add a second pass through the mount table parsing when utab is
updated.