daemon: Parse /proc/mounts instead of /etc/mtab

daemon: Parse /proc/mounts instead of /etc/mtab

Since Fedora util-linux 2.19, the %post script does:

  rm -f /etc/mtab
  ln -s /proc/mounts /etc/mtab

We are no longer running %post scripts, so this means that /etc/mtab
is a plain file in the appliance.  Usual 'mount' still updates it, but
for some reason mount.ntfs does *not* update it in Fedora 15, meaning
that you couldn't mount and then operate on NTFS partitions.

It seems better to always parse /proc/mounts (ie. what the kernel
thinks is mounted) unconditionally, rather than relying on the
capriciousness of the external mount command.

Therefore, parse /proc/mounts instead of /etc/mtab, but add a note
saying that in future we should really be parsing
/proc/self/mountinfo, but that needs a custom parser, and the format
is rather tricky:

http://lxr.linux.no/#linux+v2.6.37/Documentation/filesystems/proc.txt#L1462