Lower log severity of expected exception for authentication on unsecured instance

All unsecured instances report an INFO log at startup and on additional requests due to the Kerberos authentication mechanism being unavailable. This log severity should be lowered and the message suppressed by default as it is an expected scenario but causes concern for many users.

2020-07-17 11:37:38,023 INFO [NiFi Web Server-18] o.a.n.w.m.IllegalStateExceptionMapper java.lang.IllegalStateException: Access tokens are only issued over HTTPS. Returning Conflict response.

A follow-on Jira should address removing the unnecessary request entirely.