RemoteBlockedIOException WARN logged for every content request to manual or auto blocked repository should be TRACE

1. In Nexus 3.12.1, create a proxy repository.
2. Set "block outbound connections on the repository" to true.
3. Fire a request to the repository.

You will see a warning like this in the log:

2018-06-26 14:30:18,863-0500 WARN [qtp335821775-220] admin org.sonatype.nexus.repository.maven.internal.proxy.MavenProxyFacet - Exception org.sonatype.nexus.repository.httpclient.RemoteBlockedIOException: Remote Manually Blocked checking remote for update, proxy repo maven-central failed to fetch foo/bar/maven-metadata.xml, content not in cache.

This will be repeated for every single request received by the proxy, filling the logs with useless messages.

Expected:

This should be logged at DEBUG, if at all. Upon closer review moving the level to TRACE seems better since the blocked status of a repository can be easily determined from other INFO level log messages and the repository status is also visible when viewing the repositories list in the UI.