Prefix file should be asked once per sesssion

[cstamas]

Affected version

master

Bug description

We have reposes that today return 401, 403, 503 etc. Any prefix file should be asked only once per session, right now those are retried,

[cstamas]

This was wrong conclusion: some were retried, and usually those like plexus-snapshots, that are hosted on NX2 at oss.sonatype.org and repository was decommissioned, but was returning HTTP 503 that is not cached by Resolver. It was fixed to return 404.