This is related to elastic/x-pack-elasticsearch#1217. This PR removes the default password of
"changeme" from the reserved users.
This PR adds special behavior for authenticating the reserved users. No
ReservedRealm user can be authenticated until its password is set. The
one exception to this is the elastic user. The elastic user can be
authenticated with an empty password if the action is a rest request
originating from localhost. In this scenario where an elastic user is
authenticated with a default password, it will have metadata indicating
that it is in setup mode. An elastic user in setup mode is only
authorized to execute a change password request.
Original commit: elastic/x-pack-elasticsearch@e1e101a237
f2cbe20ea0