NEXUS-5849: Fix
NEXUS-5849: Sharing the blacklist check

Pulled up the method call to check for remote server.
NEXUS-5849: Improving message
NEXUS-5849: OMG, Friday afternoon
Merge remote-tracking branch 'origin/master' into nexus-5849-artifactory-autorouting
NEXUS-5849: Mock was incomplete causing NPE
NEXUS-5849: Test adapted

Essence is same, "connection was refused", but this time it's detected before
nexus transport is consulted (transport error), instead the usual
java ioex message is sent, "connection to XXXX refused".

Assertion adapted accordingly.
NEXUS-5849: improvement for better message handling

The method checking for blacklist is throwing now
exception if needed.
Removed comments
Merge pull request #107 from sonatype/nexus-5849-artifactory-autorouting

NEXUS-5849: Central prefix file is served through Artifactory, which results in non-central artifacts being blocked