Remove fixed string in the image name

With 'tost' hard coded here, Jenkins can't get correct repo even after setting DOCKER_REPOSITORY.
Also set the default image name to sdfabric-onos.

Change-Id: Ieb2fb6541dd69845e4f6a20c38567152b92e3a1b
diff --git a/Makefile b/Makefile
index 94d2ae7..ba5c4ff 100644
--- a/Makefile
+++ b/Makefile
@@ -22,7 +22,7 @@
 
 # Docker related
 DOCKER_REGISTRY              ?=
-DOCKER_REPOSITORY            ?=
+DOCKER_REPOSITORY            ?= sdfabric-onos
 DOCKER_BUILD_ARGS            ?=
 DOCKER_TAG                   ?= stable
 DOCKER_TAG_BUILD_DATE        ?=
@@ -69,7 +69,7 @@
 USE_LOCAL_SNAPSHOT_ARTIFACTS ?=
 
 # TOST related
-TOST_IMAGENAME               := ${DOCKER_REGISTRY}${DOCKER_REPOSITORY}tost:${DOCKER_TAG}${DOCKER_TAG_PROFILER}${DOCKER_TAG_BUILD_DATE}
+TOST_IMAGENAME               := ${DOCKER_REGISTRY}${DOCKER_REPOSITORY}:${DOCKER_TAG}${DOCKER_TAG_PROFILER}${DOCKER_TAG_BUILD_DATE}
 export LOCAL_APPS            := local-apps
 
 # Trellis-Control related