Add unittest framework + tests for wrapper scripts

This commit adds a framework for running unittests on tempest to
verify that tempest works as expect. The first tests added are to
verify the response codes of the test runner wrapper scripts we use
on jenkins jobs.

Change-Id: If8e91238054593999e7b5bc34da499bd0ac02311
diff --git a/doc/source/index.rst b/doc/source/index.rst
index 00c4e9a..f70cdd1 100644
--- a/doc/source/index.rst
+++ b/doc/source/index.rst
@@ -32,6 +32,7 @@
    field_guide/stress
    field_guide/thirdparty
    field_guide/whitebox
+   field_guide/unit_tests
 
 ------------------
 API and test cases