findmnt: add --nocanonicalize to avoid realpath()

 * in some cases is realpath() overkill
 * sometimes you want to search for explicitly specified paths (e.g.
   "findmnt --fstab /mnt/symlink") rather than for real paths
 * you want to avoid readlink() and stat() on NFS

Signed-off-by: Karel Zak <kzak@redhat.com>