prepare for flake8 gate job

Change-Id: I5eb4bd47cda6ccd8c428cee93ad33aced637fa8d

ospurge/ospurge.py

@@ -103,7 +103,7 @@ def retry(service_name):
             while True:
                 try:
                     return func(*args, **kwargs)
-                except Exception as e:
+                except Exception:
                     if n == RETRIES:
                         raise DeletionFailed(service_name)
                     n += 1

tox.ini

@@ -24,6 +24,8 @@ commands = flake8
 commands = {posargs}
 
 [flake8]
+# E501 line too long
+ignore = E501
 show-source = True
 exclude = .venv,.tox,dist,doc,*egg,build