fix(local-cluster): check to see if kubelet is running

scripts/local-cluster.sh

@@ -82,6 +82,10 @@ verify_prereqs() {
     error_exit "Can't connect to 'docker' daemon."
   fi
 
+  if docker inspect kubelet >/dev/null 2>&1 ; then
+    error_exit "Kubernetes is already running"
+  fi
+
   $KUBECTL version --client >/dev/null || download_kubectl
 }
 
@@ -99,7 +103,7 @@ get_latest_version_number() {
 
 # Detect ip address od docker host
 detect_docker_host_ip() {
-  if [ -n "${DOCKER_HOST:-}" ]; then
+  if [[ -n "${DOCKER_HOST:-}" ]]; then
     awk -F'[/:]' '{print $4}' <<< "$DOCKER_HOST"
   else
     ifconfig docker0 \