Pin Ansible to <2.4

Ansible 2.4 is scheduled for release in september [1] and changes a lot
of things we might not be ready for.
Let's just make sure we control when we want to upgrade to 2.4.

The latest release of ARA, 0.14.2, does not currently support Ansible 2.4.
The support for Ansible 2.4 will likely come in 1.0.

[1]: https://github.com/ansible/ansible/blob/b3f2d1befe509614febc28d1bf1734cb2cc50ac0/docs/docsite/rst/roadmap/ROADMAP_2_4.rst

Change-Id: Icd9b847d4e75c509aba0c3a060bb6eedfd9be257
1 file changed