Bump minimum Ansible version to 2.5

This is necessary for some Ansible tests which were renamed in 2.5 -
including 'version' and 'successful'.

Change-Id: Iacf88ef5589c7571fcf56ba8b99d3dbe76975195

ansible/roles/prechecks/vars/main.yml

 ---
 docker_version_min: '1.10.0'
 docker_py_version_min: '2.0.0'
-ansible_version_min: '2.4.0'
+ansible_version_min: '2.5.0'

doc/source/user/quickstart.rst

@@ -96,7 +96,7 @@ If not installing Kolla Ansible in a virtual environment, skip this section.
       pip install -U pip
 
 #. Install `Ansible <http://www.ansible.com>`__. Currently, Kolla Ansible
-   requires Ansible 2.4+.
+   requires Ansible 2.5+.
 
    .. code-block:: console
 
@@ -128,7 +128,7 @@ If installing Kolla Ansible in a virtual environment, skip this section.
       sudo pip install -U pip
 
 #. Install `Ansible <http://www.ansible.com>`__. Currently, Kolla Ansible
-   requires Ansible 2.4+.
+   requires Ansible 2.5+.
 
    For CentOS or RHEL, run:
 

releasenotes/notes/ansible-min-2.5-7fa76f625bf9f359.yaml

+---
+upgrade:
+  - |
+    Updates the minimum required version of Ansible to 2.5.

tools/setup_gate.sh

@@ -92,7 +92,7 @@ function setup_ansible {
     RAW_INVENTORY=/etc/kolla/inventory
 
     # TODO(SamYaple): Move to virtualenv
-    sudo -H pip install -U "ansible>=2.4" "docker>=2.0.0" "python-openstackclient" "ara<1.0.0" "cmd2<0.9.0"
+    sudo -H pip install -U "ansible>=2.5" "docker>=2.0.0" "python-openstackclient" "ara<1.0.0" "cmd2<0.9.0"
     if [[ $ACTION == "zun" ]]; then
         sudo -H pip install -U "python-zunclient"
     fi