Switch all uses of 422 response code to 400.

Switch all uses of 422 response code to 400.

The 422 response is normally only for WebDAV, and these types of
errors should normally return a 400 code, HTTPBadRequest. This
commit goes through all the remaining 422 codes and changes them
to 400 responses.

Fixes bug 1153807

Change-Id: I9bf49643763c2cb0ac585641056c85a060152e36
(cherry picked from commit adb8ba7bff2bc4e2657cf84e9f061433ff947a73)