pass the fine input to subunit2junitxml

Since python-subunut 1.2, subunit2junitxml expects an input file in the
SubUnit format 2:

  Subunit’s bundled tools accept only version 2 and only emit version 2,
  but the new filters subunit-1to2 and subunit-2to1 can be used to
  interoperate with older third party libraries.

Without any prelimiar conversion, the result will just be an empty XML
file. RHEL ships python-subunit 1.0 so we cannot just unconditionally
use the format 2 input.

Change-Id: Iab98fca8815b38283fdde44605de296d77c46b4f

roles/validate-tempest/tasks/tempest-results.yml

@@ -15,12 +15,22 @@
         | head -1) {{ working_dir }}/tempest/tempest.html \
         2>&1 >> {{ tempest_log_file }}
 
-    - name: Generate XML results file
+    - name: Test the subunit version
       shell: |
         {% if tempest_format == 'venv' %}source {{ working_dir }}/tempest_git/.venv/bin/activate; {% endif %}
-        subunit2junitxml $(find {{ working_dir }}/tempest/{{ testr_dir }} -name [0-9] \
-        | head -1) --output-to {{ working_dir }}/tempest/tempest.xml \
-        2>&1 >> {{ tempest_log_file }}
+        python -c 'import subunit; import sys; exit(int(subunit.__version__[0] <= 1 and subunit.__version__[1] <= 1))'
+      register: need_subunit1to2
+      failed_when: False
+
+    - name: Generate XML results file
+      shell: >
+        {% if tempest_format == 'venv' %}source {{ working_dir }}/tempest_git/.venv/bin/activate; {% endif %}
+        subunit2junitxml
+        {% if need_subunit1to2.rc == 0 %}
+        {{ working_dir }}/tempest/testrepository.subunit
+        {% else %}
+        $(find {{ working_dir }}/tempest/{{ testr_dir }} -name [0-9] | head -1)
+        {% endif %} --output-to {{ working_dir }}/tempest/tempest.xml 2>&1 >> {{ tempest_log_file }}
 
     - name: Fetch HTML results
       fetch: