NEXUS-5621: Blocking routing rules are not enlisted in describe

the "appliedMappings" contains both INCLUSIVE and EXCLUSIVE rules
when asked for describe a given request, but BLOCKING mappings
were not enlisted

This simple change makes sure those are enlisted too, making
it easier to detect why something is not served up (in case
BLOCKING rules are used at all).
Merge pull request #814 from sonatype/nexus-5621-blocking-routing-rule-not-in-describe

[REVIEW] NEXUS-5621: Blocking routing rules are not enlisted in describe