Add --worker-file option in tempest

This patch add the option --worker-file on tempest run command.
This will enable users to specify a worker file that will be used
by stestr to manually schedule how the tests will run.

Change-Id: I747f3abe179492da063fcaaf1123ffcf6362f966
diff --git a/releasenotes/notes/add-worker-file-option-d949121a61156968.yaml b/releasenotes/notes/add-worker-file-option-d949121a61156968.yaml
new file mode 100644
index 0000000..6b10937
--- /dev/null
+++ b/releasenotes/notes/add-worker-file-option-d949121a61156968.yaml
@@ -0,0 +1,10 @@
+---
+features:
+  - |
+    Add the option --worker-file in ``tempest run`` command. This is to give
+    tempest more granularity to manually configure how the different sets of
+    tests can be grouped to run with the different worker. You can configure
+    tests regex to run under workers. You can also mix manual scheduling with
+    standard one by mentioning concurrency.
+    For example, the user can setup tempest to run with different concurrences,
+    to be used with different regexps.