Look for python3 by default

This patch improves the required package installing task - search
first for a py3 and verify a virtualenv package is installed too.
If no py3, check py2 and py2 virtualenv respectively.

Change-Id: I7abc59f2edb0c4409ea67ac4b611a95779bef714

tasks/install-packages.yaml

@@ -1,42 +1,44 @@
 ---
-- name: Is python available
-  command: "python --version"
+- name: Is python3 available
+  command: "python3 --version"
   ignore_errors: true
-  register: python_is_available
+  register: python3_is_available
   changed_when: false
 
+- name: Is python2 available
+  command: "python2 --version"
+  ignore_errors: true
+  changed_when: false
+  when: python3_is_available.failed
+
 - name: Install git
   become: true
   package:
     name: git
 
-- name: Install virtualenv
-  become: true
-  package:
-    name: python-virtualenv
-  when: python_is_available.rc == 0
-
-- name: Install virtualenv
+- name: Install virtualenv (py3)
   become: true
   package:
     name: python3-virtualenv
-  when: python_is_available.rc != 0
+  when: not python3_is_available.failed
+
+- name: Install virtualenv (py2)
+  become: true
+  package:
+    name: python-virtualenv
+  when: python3_is_available.failed
 
 - name: Check if pip is already installed
   command: "pip --version"
   ignore_errors: true
   register: pip_is_installed
-  changed_when: false
-
-- name: Check if pip3 is already installed
-  command: "pip3 --version"
-  ignore_errors: true
-  register: pip3_is_installed
-  changed_when: false
+  when: python3_is_available.failed
 
+# pip3 is a dependency of a python3 package, so if there is a python3
+# installed, pip3 should be installed already as well
 - when:
+    - python3_is_available.failed
     - pip_is_installed.rc != 0
-    - pip3_is_installed.rc != 0
   block:
     - name: download get-pip.py
       get_url: url=https://bootstrap.pypa.io/get-pip.py  dest=/tmp

tasks/main.yaml

@@ -30,5 +30,5 @@
 - name: Check if we passed refstack tests
   fail:
     msg: "Refstack tests failed."
-  # the refstack_result var got set in run_refstack_client.yaml
+  # the refstack_result var got set in run-refstack-client.yaml
   when: refstack_result.rc > 0

tasks/run-refstack-client.yaml

@@ -46,5 +46,8 @@
     chdir: "{{ refstack_client_source }}"
     executable: /bin/bash
   register: refstack_result
+  # don't fail here in order to allow post_tasks be executed,
+  # the refstack_result is inspected in the last task of the role where it
+  # fails if it failed here
   ignore_errors: true
   when: test_list is not defined