Don't always run mount-master-pd

cluster/gce/configure-vm.sh

@@ -151,6 +151,10 @@ stop-salt-minion() {
 # formats an unformatted disk, and mkdir -p will leave a directory be if it
 # already exists.
 mount-master-pd() {
+  # TODO(zmerlynn): GKE is still lagging in master-pd creation
+  if [[ ! -e /dev/disk/by-id/google-master-pd ]]; then
+    return
+  fi
   device_info=$(ls -l /dev/disk/by-id/google-master-pd)
   relative_path=${device_info##* }
   device_path="/dev/disk/by-id/${relative_path}"