chore(db): ensure mem db behaves like mysql db
chore(db): ensure mem db behaves like mysql db

In 06554f5599fb167bcdf79c8586f2d7c9ab87643e, we temporarily disabled
insertion of device commands into the MySQL db. We didn't do the same
with the memory db though, which means the auth server tests see
different behaviour depending on which backend they're running against.
This change forces the memory backend to behave the same.

mozilla/fxa-auth-db-mysql,mozilla/fxa-auth-db-mysql