API: Allow for format modules that cannot handle errors

ApiFormatFeedWrapper, for example, has nothing particularly useful to do
when given an API error to print. So allow for punting errors to the
default formatter instead.

Bug: 63150
Change-Id: Ifc034d4c7861905e382c42dc22585f0cd2beaf3f
Merge "API: Allow for format modules that cannot handle errors"