Add cleanup to cliff-based cli framework

Also disable ability to run script in stand-alone mode so
users will use 'tempest cleanup' instead.

Change-Id: I2119acd402b0985d4a81c85501ce7265f782d37b
Implements: blueprint tempest-cli-improvements
diff --git a/setup.cfg b/setup.cfg
index 46e21f1..ee61788 100644
--- a/setup.cfg
+++ b/setup.cfg
@@ -34,6 +34,7 @@
     tempest = tempest.cmd.main:main
 tempest.cm =
     init = tempest.cmd.init:TempestInit
+    cleanup = tempest.cmd.cleanup:TempestCleanup
 oslo.config.opts =
     tempest.config = tempest.config:list_opts