only add --container-runtime if it is set

hack/jenkins/common.sh

@@ -301,7 +301,7 @@ if test -f "${TEST_OUT}"; then
 fi
 touch "${TEST_OUT}"
 
-if [ -z "${CONTAINER_RUNTIME}" ]
+if [ ! -z "${CONTAINER_RUNTIME}" ]
 then
     EXTRA_START_ARGS="${EXTRA_START_ARGS} --container-runtime=${CONTAINER_RUNTIME}"
 fi

hack/jenkins/linux_integration_tests_podman.sh

@@ -28,12 +28,11 @@ set -e
 OS_ARCH="linux-amd64"
 VM_DRIVER="podman"
 JOB_NAME="Experimental_Podman_Linux"
+CONTAINER_RUNTIME="containerd"
 
 mkdir -p cron && gsutil -qm rsync "gs://minikube-builds/${MINIKUBE_LOCATION}/cron" cron || echo "FAILED TO GET CRON FILES"
 sudo install cron/cleanup_and_reboot_Linux.sh /etc/cron.hourly/cleanup_and_reboot || echo "FAILED TO INSTALL CLEANUP"
 
-EXTRA_START_ARGS="--container-runtime=containerd"
-
 # remove possible left over podman containers
 sudo podman rm -f -v $(sudo podman ps -aq) || true