Add run_stress to cliff-based cli framework

Also disable ability to run script in stand-alone mode. So users need to
use 'tempest run-stress' instead.

Change-Id: I3effd1b71b2375f75a11f5924205741be0903361
Implements: blueprint tempest-cli-improvements
diff --git a/setup.cfg b/setup.cfg
index ee61788..4415063 100644
--- a/setup.cfg
+++ b/setup.cfg
@@ -35,6 +35,7 @@
 tempest.cm =
     init = tempest.cmd.init:TempestInit
     cleanup = tempest.cmd.cleanup:TempestCleanup
+    run-stress = tempest.cmd.run_stress:TempestRunStress
 oslo.config.opts =
     tempest.config = tempest.config:list_opts