create the image if it doesn't exist on host

Docker-DCO-1.1-Signed-off-by: Aaron Feng aaron.feng@gmail.com (github: aaronfeng)
go fmt

Docker-DCO-1.1-Signed-off-by: Aaron Feng aaron.feng@gmail.com (github: aaronfeng)
Merge branch 'master' of github.com:docker/libswarm into dockerclient-create-container

Conflicts:
	backends/dockerclient.go
Merge pull request #105 from aaronfeng/dockerclient-create-container