update sysutils/ansible to 2.7.0

This is a major release. Please see changelog and migration guide:

https://github.com/ansible/ansible/blob/2.7/changelogs/CHANGELOG-v2.7.rst
https://docs.ansible.com/ansible/devel/porting_guides/porting_guide_2.7.html

This also introduces sysutils/ansible26, which will track the 2.6 stable
branch.