Optional cf support

Docker-DCO-1.1-Signed-off-by: Mangled Deutz <olivier@webitup.fr> (github: dmp42)
Flake

Docker-DCO-1.1-Signed-off-by: Mangled Deutz <olivier@webitup.fr> (github: dmp42)
Capture stream write error

Docker-DCO-1.1-Signed-off-by: Mangled Deutz <olivier@webitup.fr> (github: dmp42)
Fix test

Docker-DCO-1.1-Signed-off-by: Mangled Deutz <olivier@webitup.fr> (github: dmp42)
Merge pull request #389 from dotcloud/0.7-Cloudfront

Optional cf support