Update DisablePasswordAuth to False does not work

• POST to update db config DisablePasswordAuth to true works, but if POST again to set back to false, returns 201 Created but does not update the field.
• Tested on master (3.1), possibly also in 3.0.1 due to backport
• Possibly related to work on:
  https://issues.couchbase.com/browse/CBG-2026
• Possibly related to field `bool` vs `*bool`
  https://github.com/couchbase/sync_gateway/blob/master/rest/config.go#L145

Initial state

Update to true

Update to false