Imports of package cancellable

PathSynopsis
github.com/docker/engine-api/client/transportPackage transport provides function to send request to remote endpoints.
golang.org/x/net/contextPackage context defines the Context type, which carries deadlines, cancellation signals, and other request-scoped values across API boundaries and between processes.
ioPackage io provides basic interfaces to I/O primitives.
net/httpPackage http provides HTTP client and server implementations.