Merge branch 'grpc-go-1.9.1' into 'master'

go/vendor/github.com/golang/protobuf/ptypes/any.go

go/vendor/github.com/golang/protobuf/ptypes/doc.go

go/vendor/github.com/golang/protobuf/ptypes/duration.go

...github.com/golang/protobuf/ptypes/duration/duration.pb.go

...github.com/golang/protobuf/ptypes/duration/duration.proto

go/vendor/github.com/golang/protobuf/ptypes/regen.sh

go/vendor/github.com/golang/protobuf/ptypes/timestamp.go

go/vendor/google.golang.org/grpc/AUTHORS

go/vendor/google.golang.org/grpc/CONTRIBUTING.md

go/vendor/google.golang.org/grpc/LICENSE

go/vendor/google.golang.org/grpc/Makefile

go/vendor/google.golang.org/grpc/PATENTS

go/vendor/google.golang.org/grpc/README.md

go/vendor/google.golang.org/grpc/backoff.go

go/vendor/google.golang.org/grpc/balancer.go

go/vendor/google.golang.org/grpc/balancer/balancer.go

go/vendor/google.golang.org/grpc/balancer/base/balancer.go

go/vendor/google.golang.org/grpc/balancer/base/base.go

.../google.golang.org/grpc/balancer/roundrobin/roundrobin.go

go/vendor/google.golang.org/grpc/balancer_conn_wrappers.go