Fix Hub API test branch checkout (konveyor#132)

Updating script checking out hub API tests to be able checkout diverged
branches (previous git pull command failed on this).

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

hub-api/run-tests.sh

@@ -26,6 +26,6 @@ if [ ! -d $HUB_TMP_DIR ]; then
 fi
 
 cd $HUB_TMP_DIR
-git pull origin ${BRANCH}
+git checkout -b api-tests-run origin/${BRANCH}
 
 make test-api