introduce --enable-fs cli option

Finally add --enable-fs option to specify the comma separated list of
filesystem names which should be treated as FSTYPE_AUTO.

Note: obviously this option is not safe, use at your own risk. "dump"
will always succeed if the mntpoint is auto, but "restore" can fail or
do something wrong if mount(src, mountpoint, flags, options) can not
actually "just work" as FSTYPE_AUTO logic expects.

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