Log deletion errors in  clean servers

Although we don't want to cause tempest to fail on error while deleting
a server in tearDownClass as these types of issues are hard to debug. We
should at least log the issues instead of hiding them completely.

Change-Id: Id0c172e247ecfcd4eec85bafd4787e33944cee1a
Related-Bug: #1372696
diff --git a/tempest/api/compute/base.py b/tempest/api/compute/base.py
index 7e9fe92..9f91bb1 100644
--- a/tempest/api/compute/base.py
+++ b/tempest/api/compute/base.py
@@ -144,14 +144,19 @@
         for server in cls.servers:
             try:
                 cls.servers_client.delete_server(server['id'])
-            except Exception:
+            except exceptions.NotFound:
+                # Something else already cleaned up the server, nothing to be
+                # worried about
                 pass
+            except Exception:
+                LOG.exception('Deleting server %s failed' % server['id'])
 
         for server in cls.servers:
             try:
                 cls.servers_client.wait_for_server_termination(server['id'])
             except Exception:
-                pass
+                LOG.exception('Waiting for deletion of server %s failed'
+                              % server['id'])
 
     @classmethod
     def server_check_teardown(cls):