fix(agent): Start/stop units asynchronously
fix(agent): Start/stop units asynchronously

Fix #466

thepwagner/fleet,mookjp/fleet,flandr/fleet,wuqixuan/fleet,dalbani/fleet,mwitkow/fleet,mwhooker/fleet,jonboulle/fleet,esatterwhite/fleet,webwlsong/fleet,improbable-io/fleet,ecnahc515/fleet,jonboulle/fleet,mookjp/fleet,mwhooker/fleet,paveltiunov/fleet,improbable-io/fleet,dongsupark/fleet,bviswana101/fleet,dalbani/fleet,coreos/fleet,giantswarm/fleet,jonboulle/fleet,paveltiunov/fleet,coreos/fleet,dongsupark/fleet,endocode/fleet,endocode/fleet,esatterwhite/fleet,bcwaldon/fleet,coreos/fleet,bcwaldon/fleet,ecnahc515/fleet,dalbani/fleet,endocode/fleet,hhoover/fleet,hhoover/fleet,giantswarm/fleet,mischief/fleet,flandr/fleet,mwitkow-io/fleet,bviswana101/fleet,mwitkow-io/fleet,dongsupark/fleet,bcwaldon/fleet,mwitkow/fleet,WPMedia/fleet,WPMedia/fleet,webwlsong/fleet,ecnahc515/fleet,octoblu/fleet,octoblu/fleet,giantswarm/fleet,thepwagner/fleet,wuqixuan/fleet,mischief/fleet,improbable-io/fleet