Fix formatter error generation
Fix formatter error generation

The result may not be a subclass of Base, so don't try to use our
formatting codes if the requested output format is not available.

Change-Id: I492b288310060b105d1e3b0f7b5717d45da467d9

quattor/aquilon,quattor/aquilon,guillaume-philippon/aquilon,quattor/aquilon,guillaume-philippon/aquilon,guillaume-philippon/aquilon