Improve error messages in validation cases. (#1812)
Improve error messages in validation cases. (#1812)

* Improve error messages in validation cases.

* Add challenge type to error detail.

This makes the errors easier to search for.

* %v->%s

* Revert boulder-config to master.

benileo/boulder,lucasallan/boulder,sophie-h/boulder,ibukanov/boulder,jfrazelle/boulder,benileo/boulder,letsencrypt/boulder,sophie-h/boulder,jfrazelle/boulder,ZCloud-Firstserver/boulder,letsencrypt/boulder,jsha/boulder,jcjones/boulder,ibukanov/boulder,ZCloud-Firstserver/boulder,letsencrypt/boulder,bmw/boulder,jcjones/boulder,ibukanov/boulder,lucasallan/boulder,ZCloud-Firstserver/boulder,jfrazelle/boulder,ZCloud-Firstserver/boulder,bmw/boulder,sophie-h/boulder,lucasallan/boulder,benileo/boulder,jsha/boulder,benileo/boulder,jcjones/boulder,jcjones/boulder,bmw/boulder,jsha/boulder,jfrazelle/boulder