Bug 30275: (follow-up) Drop renewer_id constraint

Bug 30275: (follow-up) Drop renewer_id constraint

This patch fixes some unit tests by ensureing we set a valid userid for
mock userenv setting so that the foreign key constraint doesn't fail and
it also removes the exception class and check for renewer_id from the
store method as, for example with autorenewals, the renewal may not have
been triggered by a actual user.

Signed-off-by: Tomas Cohen Arazi <tomascohen@theke.io>