Log Message:
ansible2: Update to 2.6.4.

There are a huge number of changes listed since 2.3.0.0 with thousands
of entries split over multiple changelogs spanning 4 major releases, so
those interested in the changes are invited to view the following URLs:

  https://github.com/ansible/ansible/blob/stable-2.3/CHANGELOG.md
  https://github.com/ansible/ansible/blob/stable-2.4/CHANGELOG.md
  https://github.com/ansible/ansible/blob/stable-2.5/changelogs/CHANGELOG-v2.5.rst
  https://github.com/ansible/ansible/blob/stable-2.6/changelogs/CHANGELOG-v2.6.rst