ext2fs: check if Lustre filesystem is mounted

ext2fs: check if Lustre filesystem is mounted

Add a check to ext2fs_check_mount_point() to loo in /proc/fs/lustre/*
to see if Lustre is mounted, since st_rdev of the mountpoint does not
match st_rdev of the block device itself, which confuses libext2fs.

  LU-6093 ext2fs: don't confuse mke2fs by Lustre zfs mount

  check_if_lustre_mounted() by efb735 will mistakenly report the
  device is mounted when there is a ZFS-based Lustre mount.

  This patch fix it by parsing the real device name from the pool
  name exported in Lustre proc file with "zpool" command.

  It also includes a typo fix in check_if_lustre_mounted() and a
  few other code cleanups.

  Signed-off-by: Niu Yawei <yawei.niu@intel.com>
  Change-Id: I43dabbcd6fa721c569cd9cc0f4a6de93ab761392
  Reviewed-on: http://review.whamcloud.com/14223
  Reviewed-by: John L. Hammond <john.hammond@intel.com>
Signed-off-by: Andreas Dilger <andreas.dilger@intel.com>