Major Description
This change enables the use of HadoopGroupProvider identity-assertion provider to be configured by GatewayConfig rather than having to redundantly configure it in each topology that hosts the KNOX service.
It allows for the configuration to be standard hadoop names with a "gateway.knox.admin.group.config." prefix. It is aligned with the KNOX_ADMIN_USERS and KNOX_ADMIN_GROUPS that were added to the AclsAuthz provider to allow that configuration to also be provided in the gateway config.
In Ambari managed environments this will be easier for providing this config in one place and not even need to be able to manage manager.xml or others that need this information.