Make API tests using HUB_TESTS_REF variable (#61)

* Make API tests using HUB_TESTS_REF variable

Adding HUB_TESTS_REF variable to make test-api target to (optionally) set
Hub API tests branch.

Related to konveyor/ci#22 and konveyor/ci#23

Signed-off-by: Marek Aufart <maufart@redhat.com>

* Replace ununsed BRANCH var

Signed-off-by: Marek Aufart <maufart@redhat.com>

---------

Signed-off-by: Marek Aufart <maufart@redhat.com>

Makefile

@@ -1,6 +1,5 @@
 VENDOR_DIR ?= /tmp/konveyor-vendor
 ARCH ?= amd64
-BRANCH ?= main
 
 
 # Setup local minikube with tackle - work in progress (TODO: enable auth)
@@ -64,7 +63,7 @@ test-jira:
 
 # Hub API remote tests.
 test-hub-api:
-	./hub-api/run-tests.sh ${BRANCH}
+	./hub-api/run-tests.sh ${HUB_TESTS_REF}
 
 # Add next features tests here and call the target from appropriate stage.