Fail a test if stack delete failed

Whenever a deleting stack goes to DELETE_FAILED this is an error which should fail
the test. Currently delete failures are ignored. As a side-effect of this, delete-failed
stacks are leaked even though tests pass.

The test may have done is own assertions on stack deletes, so a NotFound
exception is still passed.

Change-Id: I5f9e5901bcbd50bd8bd38c62175755ba59c6b837
Closes-Bug: #1295415
diff --git a/tempest/api/orchestration/base.py b/tempest/api/orchestration/base.py
index 3424082..79f8f4a 100644
--- a/tempest/api/orchestration/base.py
+++ b/tempest/api/orchestration/base.py
@@ -13,6 +13,7 @@
 from tempest import clients
 from tempest.common.utils import data_utils
 from tempest import config
+from tempest import exceptions
 from tempest.openstack.common import log as logging
 import tempest.test
 
@@ -73,14 +74,14 @@
         for stack_identifier in cls.stacks:
             try:
                 cls.orchestration_client.delete_stack(stack_identifier)
-            except Exception:
+            except exceptions.NotFound:
                 pass
 
         for stack_identifier in cls.stacks:
             try:
                 cls.orchestration_client.wait_for_stack_status(
                     stack_identifier, 'DELETE_COMPLETE')
-            except Exception:
+            except exceptions.NotFound:
                 pass
 
     @classmethod