getRoles is called a lot (on every restricted access, so hundreds of times
per transaction), it is definitely not the right place to do extra
computation, especially when their result does not change from one call
to the next (configuration should only change on process restart, so not
during a transaction - and even if it someday did, it should be fine to
wait for next transaction for it to take effect).
Instead, do the extra work when creating the user (typically once per
transaction).
Also, modernise python syntax (simplifications & style).
Also, reduce code duplication from ERP5Security.ERP5UserFactory.