remove docker info warnings (if any) from Makefile

Signed-off-by: Victor Vieux <vieux@docker.com>

Makefile

@@ -1,7 +1,7 @@
 .PHONY: all binary build build-gccgo cross default docs docs-build docs-shell shell gccgo test test-docker-py test-integration-cli test-unit validate help
 
 # set the graph driver as the current graphdriver if not set
-DOCKER_GRAPHDRIVER := $(if $(DOCKER_GRAPHDRIVER),$(DOCKER_GRAPHDRIVER),$(shell docker info | grep "Storage Driver" | sed 's/.*: //'))
+DOCKER_GRAPHDRIVER := $(if $(DOCKER_GRAPHDRIVER),$(DOCKER_GRAPHDRIVER),$(shell docker info 2>&1 | grep "Storage Driver" | sed 's/.*: //'))
 
 # get OS/Arch of docker engine
 DOCKER_OSARCH := $(shell bash -c 'source hack/make/.detect-daemon-osarch && echo $${DOCKER_ENGINE_OSARCH:-$$DOCKER_CLIENT_OSARCH}')