We ignored errors for simple syntax in `PortOpt` (missed that in the
previous migration of this code). This make sure we don't ignore
`nat.Parse` errors.
Test has been migrate too (errors are not exactly the same as before
though -_-)
Signed-off-by: Vincent Demeester <vincent@sbr.pm>
`--publish-add 8081:81 --publish-add 8082:82 --publish-rm 80
--publish-rm 81/tcp --publish-rm 82/tcp` would thus result in 81 and
82 to be published.
Signed-off-by: Vincent Demeester <vincent@sbr.pm>