Change LOG.exception to LOG.info for skipped tests

The safe setup decorator was presenting skipException in the logs as an error
and so producing lot of noise in tempest.log.

Change-Id: Ia95d6b9dee4eaf4fc8de4bb128f958ef7f693844
Related-bug: #1344581
diff --git a/tempest/test.py b/tempest/test.py
index f34933e..3733d99 100644
--- a/tempest/test.py
+++ b/tempest/test.py
@@ -76,7 +76,10 @@
                 f(cls)
             except Exception as se:
                 etype, value, trace = sys.exc_info()
-                LOG.exception("setUpClass failed: %s" % se)
+                if etype is cls.skipException:
+                    LOG.info("setUpClass skipped: %s:" % se)
+                else:
+                    LOG.exception("setUpClass failed: %s" % se)
                 try:
                     cls.tearDownClass()
                 except Exception as te: