[2.8.x] NEXUS-5987: Routing fixes

Changes:
* removed "applies to user managed reposes only" limitation
* removed use of ancient "validator", migrated what was needed from it
* updated logging and other issues found in class

Backport of PR
https://github.com/sonatype/nexus-oss/pull/388

Issue
https://issues.sonatype.org/browse/NEXUS-5987

CI
https://bamboo.zion.sonatype.com/browse/NX-OSSF43