certmonger: refactor 'resubmit_request' and 'modify'
certmonger.resubmit_request() and .modify() contain a redundant if
statement that means more lines of code must be changed when adding
or removing a function argument. Perform a small refactor to
improve these functions.
Part of: https://pagure.io/freeipa/issue/6858
Reviewed-By: Florence Blanc-Renaud <frenaud@redhat.com>