NEXUS-6249: Wrong checksums cached for Maven artifact

When they get updated. While this is not a problem
in 90% of cases (as releases nor unique snapshots never
get updated), the non-unique snapshots and maven metadata
files, once cached, their initial SHA1/MD5 remote
hashes were NEVER updated.

Issue
https://issues.sonatype.org/browse/NEXUS-6249

CI
TBD