Update minimum version of Ansible to 2.6

This is required for the dict2items filter.

Change-Id: I60a04e839bf06506ff36c2631a286130d5fde972

ansible/roles/prechecks/vars/main.yml

@@ -1,4 +1,4 @@
 ---
 docker_version_min: '1.10.0'
 docker_py_version_min: '2.0.0'
-ansible_version_min: '2.5.0'
+ansible_version_min: '2.6.0'

doc/source/user/quickstart.rst

@@ -90,7 +90,7 @@ 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 2.5+.
+   requires Ansible 2.6+.
 
    .. code-block:: console
 
@@ -122,7 +122,7 @@ 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 2.5+.
+   requires Ansible 2.6+.
 
    For CentOS or RHEL, run:
 

releasenotes/notes/ansible-min-2.6-4b96795a1cc4b6b2.yaml

@@ -0,0 +1,4 @@
+---
+upgrade:
+  - |
+    Updates the minimum required version of Ansible to 2.6.

tools/setup_gate.sh

@@ -113,9 +113,9 @@ function setup_ansible {
 
     # Test latest ansible version on Ubuntu, minimum supported on others.
     if [[ $BASE_DISTRO == "ubuntu" ]]; then
-        ANSIBLE_VERSION=">=2.5"
+        ANSIBLE_VERSION=">=2.6"
     else
-        ANSIBLE_VERSION="<2.6"
+        ANSIBLE_VERSION="<2.7"
     fi
 
     # TODO(SamYaple): Move to virtualenv