Better exception re-raising

re-raising the exception without specifying the exception object gives
exactly the previous exception (including the correct stacktrace)
which is nicer to have for debugging.

ldapcherry/__init__.py

@@ -206,7 +206,7 @@ class LdapCherry(object):
                     key,
                     )
             except MissingParameter as e:
-                raise e
+                raise
             except Exception as e:
                 self._handle_exception(e)
                 raise BackendModuleInitFail(module)