dump/restore fstype->name if FSTYPE__AUTO

Add the new mnt_entry->fsname member and change dump_one_mountpoint()
to save pm->fstype->name if fstype == FSTYPE__AUTO.

Change collect_mnt_from_image() to pass this ->fsname to decode_fstype()
which falls back to __find_fstype_by_name(fsname, true) if FSTYPE__AUTO.

Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Signed-off-by: Pavel Emelyanov <xemul@parallels.com>