Add build-docker target in Makefile

Change-Id: I7194c57e270493ac3b384a257a7b5b93b979ae96
Signed-off-by: abhay <abhayk@radisys.com>
diff --git a/Makefile b/Makefile
index 239fe04..376b7e0 100644
--- a/Makefile
+++ b/Makefile
@@ -91,6 +91,8 @@
 	@echo Building vgcctl....
 	@cd voltha-go-controller/cli && go build -o vgcctl
 
+docker-build: exe vgcctl
+
 docker: exe vgcctl
 	@echo Building Docker $(DOCKER_NAME)....
 	sudo docker build -t $(IMAGENAME) -f docker/Dockerfile.voltha-go-controller .