Add more information to BuildErrorException

This commit adds expected_status to BuildErrorException. This is helpful
for checking the error details.

Change-Id: I2979d39467daeb06793081b83e3a5b81b7d5623e
Closes-bug: #1265559
diff --git a/tempest/scenario/manager.py b/tempest/scenario/manager.py
index 59a3aeb..4937a4e 100644
--- a/tempest/scenario/manager.py
+++ b/tempest/scenario/manager.py
@@ -395,8 +395,9 @@
             # so case sensitive comparisons can really mess things
             # up.
             if new_status.lower() == error_status.lower():
-                message = ("%s failed to get to expected status. "
-                           "In %s state.") % (thing, new_status)
+                message = ("%s failed to get to expected status (%s). "
+                           "In %s state.") % (thing, expected_status,
+                                              new_status)
                 raise exceptions.BuildErrorException(message,
                                                      server_id=thing_id)
             elif new_status == expected_status and expected_status is not None: