Godeps: Bump docker and libcontainer packages

Signed-off-by: Jonathan Rudenberg <jonathan@titanous.com>
host: Remove unused docker-specific interface in attach.go.

Signed-off-by: Blaž Hrastnik <blaz.hrast@gmail.com>
host: Use upstream go-dockerclient.

Signed-off-by: Blaž Hrastnik <blaz.hrast@gmail.com>