Switch from AuthService::userExists to AuthService::userExistsInConf
or AuthService::userExistsInConfOrAuth

Signed-off-by: Etienne CHAMPETIER <etienne.champetier@fiducial.net>
Change CACHE_MASTER_USERS_TO_SLAVE default to false

We shouldn't need this hack anymore

Signed-off-by: Etienne CHAMPETIER <etienne.champetier@fiducial.net>
Deprecate AuthService::userExists and AuthService::listUsers

Signed-off-by: Etienne CHAMPETIER <etienne.champetier@fiducial.net>