Imports of networkdb-test command

PathSynopsis
contextPackage context defines the Context type, which carries deadlines, cancellation signals, and other request-scoped values across API boundaries and between processes.
github.com/containerd/logPackage log provides types and functions related to logging, passing loggers through a context, and attaching context to the logger.
github.com/docker/docker/libnetwork/cmd/networkdb-test/dbclient
github.com/docker/docker/libnetwork/cmd/networkdb-test/dbserver
osPackage os provides a platform-independent interface to operating system functionality.