log: replace grpc logger with logrus

Signed-off-by: Stephen J Day <stephen.day@docker.com>

log/grpc.go

@@ -0,0 +1,8 @@
+package log
+
+import "google.golang.org/grpc/grpclog"
+
+func init() {
+	// completely replace the grpc logger with the logrus logger.
+	grpclog.SetLogger(L)
+}