Pin get-pip.py to 3.2

As get-pip.py evolves based on pip 10, while we're still using
pip 9, changes in the way it can be used are causing problems.

For example, the ability to use --download is no longer there.

As such, let's pin to a known good version and leave it at that
until we no longer need to use this script. Version 3.2 maps to
pip 7.1.2 which fulfills our needs.

Change-Id: I24609eb753e8c041842bd3b0cc6d404ad9d7cb22

tasks/repo_build_wheels.yml

@@ -128,7 +128,7 @@
 
 - name: Get /opt/get-pip.py if it does not exist
   get_url:
-    url: "{{ pip_upstream_url | default('https://bootstrap.pypa.io/get-pip.py') }}"
+    url: "{{ pip_upstream_url | default('https://bootstrap.pypa.io/3.2/get-pip.py') }}"
     dest: "/opt/get-pip.py"
     force: no
   register: _get_pip