"failed content integrity validation" message when remote returns 404

https://github.com/sonatype/nexus-oss/blob/nexus-2.11.x/components/nexus-core/src/main/java/org/sonatype/nexus/proxy/repository/AbstractProxyRepository.java#L1510-1510

https://github.com/sonatype/nexus-oss/blob/nexus-2.11.x/components/nexus-core/src/main/java/org/sonatype/nexus/proxy/repository/AbstractProxyRepository.java#L1259-1259

Prints a concerning log message stating "failed content integrity validation" when in actual fact, the remote may have responded with 404 or other implied 'not found' status code.

Instead, print a log message indicating the status code and more exact reason the file was detected as not valid.

To reproduce:

1. Change logging level of ROOT to DEBUG
2. Request a file through a Maven proxy repository that the remote will return 404 for.
3. examine the logs for the message "failed content integrity validation"