* Enable string uuid as namespace
This addresses a noisy deprecation warning showing in specs (it points
to our re-implementation of warden's sign_in_as helper, but I suspect
the issue is within warden since our initializer seems to match the
implementation in the upstream gem).
My understanding of this is that the prior default had been to pass
the provided uuid namespace as-is if it didn't match one of a few
named constants. New behavior is to validate that any string provided
as a namespace looks like a uuid representation or fail).
* Move configuration change to framework defaults
