Proposed Refactorings for Client/Daemon Init

* Addition of a new method to the engine.Job struct (https://github.com/zinic/docker/blob/master/engine/job.go#L108-L110) to allow for sub-job scheduling without requiring visibility into the Job's Engine
* Relocation of daemon argument processing and startup to its own file /daemon/initjob.go (https://github.com/zinic/docker/blob/master/daemon/initjob.go) as an engine.Job
* Removal of daemon init related code from /docker/docker.go (https://github.com/zinic/docker/blob/master/docker/docker.go)
* Modification of argument processing in /docker/docker.go (https://github.com/zinic/docker/blob/master/docker/docker.go) to allow for a stepped transition to engine.Job for legacy client code
* Addition of the new daemon init job to /builtins/builtins.go (https://github.com/zinic/docker/blob/master/builtins/builtins.go)

Docker-DCO-1.1-Signed-off-by: John Hopper <john.hopper@jpserver.net> (github: zinic)