add tmp to .dockerignore
add tmp to .dockerignore

let's please add tmp to .dockerignore: it's in .gitignore and I've got a boatload of stuff there, for my local testing

gizmotronic/os,imikushin/os,ibuildthecloud/os,ibuildthecloud/os,rancherio/os,juliengk/os,SvenDowideit/os,imikushin/os,gizmotronic/os,rancher/os,SvenDowideit/os,rancherio/os,juliengk/os,rancherio/os,rancher/os