Improve test framework documentation

Change-Id: I06f0cbbbdd29e04a07f1db6807b3e16f1d41e8d2
Signed-off-by: Klement Sekera <ksekera@cisco.com>
diff --git a/test/doc/util.rst b/test/doc/util.rst
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+util module
+===========
+
+.. automodule:: util
+    :members:
+    :undoc-members:
+    :show-inheritance: