Add support to tempest --worker-file option

This patch add support to tempest run --worker-file option.
This add the possibility to manually schedule how tempest tests will be
executed in each worker

Change-Id: I9ea47452c430c6bf5ec0ac6332cecd5d3abc7792

defaults/main.yml

@@ -42,6 +42,10 @@ tempest_run: no
 # Define 0 (serial) or more to use a non default concurrency
 #tempest_run_concurrency:
 
+# Define the worker file to be used by tempest
+# This worker file is parsed to stestr to manually schedule tempest tests
+# tempest_test_worker_file_path:
+
 # We comment `tempest_git_repo` so that the repo_build role does not attempt to
 # build the wheel from this repo/branch. Instead, we want tempest to get built
 # from the stable release defined in global requirements.

tasks/tempest_run.yml

@@ -27,6 +27,9 @@
       {% else %}
         --serial \
       {% endif %}
+      {% if tempest_test_worker_file_path is defined %}
+        --worker-file {{ tempest_test_worker_file_path }} \
+      {% endif %}
       {% if tempest_test_blacklist | length > 0 %}
         --blacklist-file {{ tempest_test_blacklist_file_path }} \
       {% endif %}