[Trivial]Remove unused variables

This is to remove unused variables and to use merging-isinstance.

Change-Id: I9d7121678a8b18a03b7b872526bfc74351560776
diff --git a/tempest/cmd/account_generator.py b/tempest/cmd/account_generator.py
index ff552a1..917262e 100755
--- a/tempest/cmd/account_generator.py
+++ b/tempest/cmd/account_generator.py
@@ -270,7 +270,7 @@
                 config.CONF.set_config_path(parsed_args.config_file)
             setup_logging()
             resources = []
-            for count in range(parsed_args.concurrency):
+            for _ in range(parsed_args.concurrency):
                 # Use N different cred_providers to obtain different
                 # sets of creds
                 cred_provider = get_credential_provider(parsed_args)