Run docker with sudo if necessary in iowait makefile

The solution is taken from the toplevel Makefile.

examples/plugins/iowait/Makefile

@@ -1,5 +1,6 @@
 .PHONY: run clean
 
+SUDO=$(shell docker info >/dev/null 2>&1 || echo "sudo -E")
 EXE=iowait
 IMAGE=weavescope-iowait-plugin
 UPTODATE=.$(EXE).uptodate
@@ -7,18 +8,18 @@ UPTODATE=.$(EXE).uptodate
 run: $(UPTODATE)
 	# --net=host gives us the remote hostname, in case we're being launched against a non-local docker host.
 	# We could also pass in the `-hostname=foo` flag, but that doesn't work against a remote docker host.
-	docker run --rm -it \
+	$(SUDO) docker run --rm -it \
 		--net=host \
 		-v /var/run/scope/plugins:/var/run/scope/plugins \
 		--name $(IMAGE) $(IMAGE)
 
 $(UPTODATE): $(EXE) Dockerfile
-	docker build -t $(IMAGE) .
+	$(SUDO) docker build -t $(IMAGE) .
 	touch $@
 
 $(EXE): main.go
-	docker run --rm -v "$$PWD":/usr/src/$(EXE) -w /usr/src/$(EXE) golang:1.6 go build -v
+	$(SUDO) docker run --rm -v "$$PWD":/usr/src/$(EXE) -w /usr/src/$(EXE) golang:1.6 go build -v
 
 clean:
 	- rm -rf $(UPTODATE) $(EXE)
-	- docker rmi $(IMAGE)
+	- $(SUDO) docker rmi $(IMAGE)