tasks: repo_build_wheels: Download get-pip.py if it does not exist

/opt/get-pip.py may not exist if the host uses the distribution
python-pip package. As such, we need to check if the file exists
and download it if it's missing before trying to copy it to the
repo build directory. Fixes the following problem:

==> opensuse423: TASK [repo_build : Copy get-pip script into release folder] ********************
==> opensuse423: Friday 25 May 2018  19:19:07 +0200 (0:00:01.362) 0:17:03.950 ************
==> opensuse423: fatal: [aio1_repo_container-b8bbcfc4]: FAILED! => {"changed": false, "failed": true, "msg": "Source /opt/get-pip.py not found"}

Change-Id: I693b930bf337fd08931d835d57ffe9ecae904517

tasks/repo_build_wheels.yml

@@ -118,6 +118,16 @@
     src: "requirements_absolute_requirements.txt.j2"
     dest: "{{ repo_build_release_path }}/requirements_absolute_requirements.txt"
 
+- name: Get /opt/get-pip.py if it does not exist
+  get_url:
+    url: "https://bootstrap.pypa.io/get-pip.py"
+    dest: "/opt/get-pip.py"
+    force: no
+  register: _get_pip
+  until: _get_pip | success
+  retries: 10
+  delay: 5
+
 - name: Copy get-pip script into release folder
   copy:
     src: "/opt/get-pip.py"