prechecks: check ansible version on deployment host

Change-Id: I688ac5cba128e7eae9df9f51c48273e39fdb09a9
Partially-implements: blueprint precheck-tasks

ansible/roles/prechecks/tasks/package_checks.yml

@@ -4,3 +4,8 @@
   register: result
   failed_when: result | failed or
                result.stdout | version_compare(docker_py_version_min, '<')
+
+- name: Checking Ansible version
+  local_action: command ansible --version
+  register: result
+  failed_when: result.stdout | regex_replace('ansible (\\d+\\.\\d+\\.\\d+)', '\\1') | version_compare(ansible_version_max, '>=')

ansible/roles/prechecks/vars/main.yml

@@ -1,2 +1,3 @@
 docker_version_min: '1.9.0'
 docker_py_version_min: '1.6.0'
+ansible_version_max: '2.0.0'