Adds support for Ansible 2.8, bump mimimum to 2.6

Updates the minimum version of Ansible from 2.5 to 2.6, and the maximum
supported version from 2.7 to 2.8.

Change-Id: I5aeb28424a8d1920b58ca73e37131d8cbfeabf29

ansible/kolla-ansible.yml

 ---
+- name: Gather facts for localhost
+  hosts: localhost
+  gather_facts: true
+  tags: always
+
 - name: Set interfaces for overcloud hosts
   hosts: overcloud
   tags:
@@ -213,7 +218,7 @@
   hosts: localhost
   tags:
     - kolla-ansible
-  gather_facts: true
+  gather_facts: false
   vars:
     # We need to reference configuration for the network node.
     # We pick the first host from the group for this. It is possible that at

ansible/roles/kolla-ansible/templates/requirements.txt.j2

@@ -7,7 +7,7 @@ kolla-ansible=={{ kolla_openstack_release }}
 {% endif %}
 # Limit the version of ansible used by kolla-ansible to avoid new releases from
 # breaking tested code. Changes to this limit should be tested.
-ansible>=2.5,<2.8
+ansible>=2.6,<2.9
 {% if kolla_ansible_venv_extra_requirements is defined %}
 {% for item in kolla_ansible_venv_extra_requirements %}
 {{ item }}

releasenotes/notes/ansible-2.6-2.8-ce141db0edb87e1c.yaml

+---
+upgrade:
+  - |
+    Updates the minimum supported version of Ansible from 2.5 to 2.6, and the
+    maximum supported version from 2.7 to 2.8. This is true for both Kayobe and
+    Kolla Ansible.

requirements.txt

@@ -3,7 +3,7 @@
 # process, which may cause wedges in the gate later.
 
 pbr>=2.0 # Apache-2.0
-ansible>=2.5.0,<2.8.0 # GPLv3
+ansible>=2.6.0,<2.9.0 # GPLv3
 cliff>=2.5.0,<2.15.0 # Apache
 netaddr!=0.7.16,>=0.7.13 # BSD
 PyYAML>=3.10.0 # MIT

requirements.yml

@@ -34,7 +34,7 @@
 - src: stackhpc.os-ironic-state
   version: v1.2.0
 - src: stackhpc.os-networks
-  version: v1.2.0
+  version: v1.3.1
 - src: stackhpc.os-openstackclient
   version: v1.3.0
 - src: stackhpc.os-shade