[SKIP] Load builtins dynamically.
Call the correct jobs in legacy mode
WIP add bridge and daemon builtins
WIP print defaults if there are no arguments
WIP in legacy client mode, call plugin 'restclient'
WIP fix mflag crash
WIP: cleanup opts parsing in main
WIP expose REST client as a job
[SKIP] Engine.ParseJob: create a new job from a shell-like text command.
[SKIP] Engine: register builtin command 'commands' to list all dynamically registered commands.
[SKIP] Engine: clearer job error reporting

* Job.Error and Job.Errorf always print a newline.
* Avoid redundant prefixing of error messages.
restserver: print messages on the job output instead of stdout
Improve and simplify the docker binry.

* Disable engine logging by default: no more noise on stdout.
* Code cleanup: use Engine.ParseJob to parse plugin commands.
* Allow no command argument. For example to test plugin commands.