* Renaming DOCKER_ORCHESTRATOR to DOCKER_STACK_ORCHESTRATOR
* Renaming config file option "orchestrator" to "stackOrchestrator"
* "--orchestrator" flag is no more global but local to stack command and subcommands
* Cleaning all global orchestrator code
* Replicating Hidden flags in help and Supported flags from root command to stack command
Signed-off-by: Silvin Lubecki <silvin.lubecki@docker.com>