catch and log IllegalCaseId, but accept form

fixes http://manage.dimagi.com/default.asp?147015

respond with 201, save form as XFormError

this is basically pre-atomic form submissions behavior
except that there is no chance of some of the cases getting processed
but not others
This test was actually incorrect. `submit_form_locally` would raise `IllegalCaseId` making the rest of the test unreachable. That's why the `XFormError.view` call below is different, because this one had never been run.