Improving prefix publishing logs.

Instead of log on any publishing, the outcome
of the prefix file publishing will be logged
only when given repo "transitions" itself from
one state to another (was published and is
unpublished or other way around).
Fix for intermittent NPE in routing tests.

Problem was that UT/ITs had no more means to detect
when "boot is done", and sometimes they kicked in
too early, with expectations (or without proper
checks) causing NPEs with carelessly loading
up prefix files without checking for their
existence (as "they should exist").

Reason was that boot process of routing
did not finish yet, as in 1st pass all
the prefix files are created for hosted
repositories for example.
UT that verifies that prefix files fetched from remote are unchanged

Hence, if remote does publish prefix file and this proxy got it
it should not mangle it in any way, it should just "pass it"
downstream in unmodified form
Fix for 31a61de1c08bdccd8e9611ecd975abd6ffd9ff06

As the change in commit above is true only if
feature is enabled, which is not in some tests.

This method change affects only UT/ITs.
Do not re-save prefix file onto itself.
Fix similar to 256bc869ac25fa4b6a12cb866c92c9883395b7df

Note: this method is specialized (as it's name implied)
and is not used in core, but in some plugins, like SP ;)
Merge remote-tracking branch 'origin/master' into routing-fixes
Merge remote-tracking branch 'origin/master' into routing-fixes
Merge pull request #817 from sonatype/routing-fixes

[REVIEW] Routing fixes