Bump Ansible to 2.7 for Stein testing
Bump Ansible to 2.7 for Stein testing

Stein branches now support Ceph Nautilus upstream, let's bump ansible to 2.7 which is required for it.

Depends-On: https://review.rdoproject.org/r/#/c/20157/
Change-Id: I6f08db1f49fb422da9d91d6b40b057c46f3568d8

redhat-openstack/rdoinfo,javierpena/rdoinfo