Imports of vpnkit-expose-port command

PathSynopsis
contextPackage context defines the Context type, which carries deadlines, cancellation signals, and other request-scoped values across API boundaries and between processes.
flagPackage flag implements command-line flag parsing.
github.com/moby/vpnkit/go/pkg/vpnkitPackage vpnkit allows a running VPNKit service to be reconfigured.
logPackage log implements a simple logging package.
netPackage net provides a portable interface for network I/O, including TCP/IP, UDP, domain name resolution, and Unix domain sockets.
osPackage os provides a platform-independent interface to operating system functionality.
os/signalPackage signal implements access to incoming signals.