[REVIEW] Routing fixes

Cumulative fixes for automatic routing.

Changes:
* improve logging of prefix updates (log only when repo transitions itself from published to unpublished or other way around, not ALWAYS)
* UT and fix to make proxy repositories not change downloaded prefix file, hence preserving them as-is for downstream consumption.

Already merged to master:
* fix NPE (affecting mostly routing related UTs and ITs) that makes tests unstable. There was a "hole" that made tests able to kick in too early, when booting was not finished (yet, test assertions assumed it was done).

CI
https://bamboo.zion.sonatype.com/browse/NXO-OSSF17-1