Addresses lp#942382 - refactor configuration for clarity

* Renamed 'nova' to 'compute'
* Merged 'env' with 'compute'
* Created new 'identity' section
* Added defensive code for bad configs

Change-Id: Ifd7506ed82ae2870600a8676a5e811769517a65d
diff --git a/tempest/exceptions.py b/tempest/exceptions.py
index a3fabe3..9f33740 100644
--- a/tempest/exceptions.py
+++ b/tempest/exceptions.py
@@ -27,6 +27,10 @@
         return self._error_string
 
 
+class InvalidConfiguration(TempestException):
+    message = "Invalid Configuration"
+
+
 class NotFound(TempestException):
     message = "Object not found"