Install pip3 for docker-compose installation

We need newer docker-compose for functionality like stop_grace_period
and the easiest way to get that is via pypi. To install from there we
need pip.

This also fixes pip3 to work on xenial which doesn't have a
python3-distutils package.

Change-Id: I5f5431cac7eb191f2f5443892292ca5a236fe1e6

playbooks/roles/install-docker/tasks/main.yaml

@@ -23,6 +23,10 @@
       - docker-compose
     state: absent
 
+- name: ensure pip3 is installed
+  include_role:
+    name: pip3
+
 - name: Install docker-compose
   pip:
     name: docker-compose

playbooks/roles/pip3/tasks/main.yaml

@@ -7,11 +7,14 @@
 
 # NOTE(ianw) : See https://github.com/pypa/get-pip/issues/43;
 # requirement of get-pip.py
+# Xenial doesn't have python3-distutils as it appears to be part
+# of python3 itself.
 - name: Ensure distutils
   package:
     name:
       - python3-distutils
     state: present
+  when: ansible_distribution_release != 'xenial'
 
 - name: Download get-pip.py
   command: wget https://bootstrap.pypa.io/get-pip.py