extra_hosts in the compose file format allows '=' as a separator, and brackets
around IP addresses, the engine API doesn't.
So, transform the values when reading a compose file for 'docker stack'.
Signed-off-by: Rob Murray <rob.murray@docker.com>
(cherry picked from commit c986d09bca)
Signed-off-by: Paweł Gronowski <pawel.gronowski@docker.com>