[VOL-1527] Not building the image with the voltha/ repository by default

Change-Id: I1f9d45475b33e60e88ef7c593e58381c53f4f139
diff --git a/Makefile b/Makefile
index b1e2e4e..e46cc27 100644
--- a/Makefile
+++ b/Makefile
@@ -18,7 +18,7 @@
 
 ## Docker related
 DOCKER_TAG  			?= ${VERSION}
-DOCKER_REPOSITORY  		?= voltha/
+DOCKER_REPOSITORY  		?= ""
 DOCKER_REGISTRY 		?= ""
 DOCKER_RUN_ARGS			?= ""