Support for Ansible 2.17

[upekkha]

Ansible 2.17 introduces a new ignore_unknown_opts argument, as explained in the changelog:

• modules - Add the ability for an action plugin to call self._execute_module(*, ignore_unknown_opts=True) to execute a module with options that may not be supported for the version being called. This tells the module basic wrapper to ignore validating the options provided match the arg spec.

This PR provides a minimal patch to get mitogen working with ansible 2.17.

[moreati]

refs #1074

[stefanor]

Added this patch to mitogen in Debian unstable. #1073837

[ohdearaugustin]

Also tested this locally, so far look fine to me. Please merge.