Imports of msh 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/mesos/mesos-go/api/v1/cmd/msh/appmsh is a minimal mesos v1 scheduler; it executes a shell command on a mesos agent.
logPackage log implements a simple logging package.
osPackage os provides a platform-independent interface to operating system functionality.