Move decision_maker() call into setUpClass

Previously the class level call of decision_maker() to detect certain
configuration details for the boto tests was mad in the class
definition. This has issues with unit testing because it requires a
functional config at import time for the file. This commit avoids this
restriction by moving this call into setUpClass for BotoTestCase which
won't try to execute decision_maker() at import.

Change-Id: I8abf4ae109576499fed6b31ae644c1bac58e3350
diff --git a/tempest/thirdparty/boto/test.py b/tempest/thirdparty/boto/test.py
index 5295e44..5ae21c8 100644
--- a/tempest/thirdparty/boto/test.py
+++ b/tempest/thirdparty/boto/test.py
@@ -193,11 +193,10 @@
 class BotoTestCase(tempest.test.BaseTestCase):
     """Recommended to use as base class for boto related test."""
 
-    conclusion = decision_maker()
-
     @classmethod
     def setUpClass(cls):
         super(BotoTestCase, cls).setUpClass()
+        cls.conclusion = decision_maker()
         # The trash contains cleanup functions and paramaters in tuples
         # (function, *args, **kwargs)
         cls._resource_trash_bin = {}