Fix use of except in tempest.

Ensure that except has a condition to comply with rule TEMPEST N201.

Change-Id: I96721394e5cfc31c163b3ec5ad5551f7cd5bbfab
diff --git a/tempest/tests/compute/base.py b/tempest/tests/compute/base.py
index eb8b443..5094b46 100644
--- a/tempest/tests/compute/base.py
+++ b/tempest/tests/compute/base.py
@@ -199,7 +199,7 @@
         while True:
             try:
                 condition()
-            except:
+            except Exception:
                 pass
             else:
                 return