Add specified warnings in rm option
Add specified warnings in rm option

Closes  https://github.com/docker/machine/issues/3640

Signed-off-by: Han Zhang <4ff615253469989932532e926006ae5c995e5dd6@zhanghan177.me>
londoncalling/machine,dgageot/machine,xinxian0458/machine,xinxian0458/machine,wzymaster/machine,dweomer/docker-machine,docker/machine,ibuildthecloud/machine,ibuildthecloud/machine,Herbis/machine,voutilad/machine,exoscale/docker-machine,bgokden/machine,larsla/machine,flavio/machine,Herbis/machine,voutilad/machine,exoscale/docker-machine,wzymaster/machine,menglingwei/machine,londoncalling/machine,bgokden/machine,SvenDowideit/machine,SvenDowideit/machine,menglingwei/machine,flavio/machine,bgokden/machine,dweomer/docker-machine,wzymaster/machine,xinxian0458/machine,dgageot/machine,larsla/machine,docker/machine,menglingwei/machine