Imports of metrics_client 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.
fmtPackage fmt implements formatted I/O with functions analogous to C's printf and scanf.
google.golang.org/grpcPackage grpc implements an RPC system called gRPC.
google.golang.org/grpc/credentials/insecurePackage insecure provides an implementation of the credentials.TransportCredentials interface which disables transport security.
google.golang.org/grpc/grpclogPackage grpclog defines logging for grpc.
google.golang.org/grpc/interop/stress/grpc_testing
ioPackage io provides basic interfaces to I/O primitives.