Fixes #6211,BZ1102521 - Use hidden user's remote id to ping pulp_auth

Don't ask me why but require_login doesn't actually require a login or user. It just sets User.current if credentials were passed. I tested it:

```
❯ curl "http://localhost:3000/katello/api/v2/ping"
{"status":"FAIL","services":{"elasticsearch":{"status":"ok","duration_ms":"13"},"katello_jobs":{"status":"FAIL","message":"katello-jobs service not running"},"candlepin":{"status":"ok","duration_ms":"564"},"candlepin_auth":{"status":"ok","duration_ms":"82"},"pulp":{"status":"ok","duration_ms":"21"},"pulp_auth":{}}}
```