Bind mount /var/tmp for Podman

When the CRI-O container storage backend is used, loading images using
`podman load` creates temporary files in /var/tmp. As /var/tmp is
mounted as tmpfs, these temporary files rapidly consume the available memory
and cause processes on the minikube VM to be OOM-killed.

Instead, bind mount /var/tmp like we do with /var/log, which will write
temporary files to disk instead of memory.

deploy/iso/minikube-iso/package/automount/minikube-automount

@@ -109,6 +109,10 @@ if [ -n "$BOOT2DOCKER_DATA" ]; then
     mkdir /var/log
     mount --bind /mnt/$PARTNAME/var/log /var/log
 
+    mkdir -p /mnt/$PARTNAME/var/tmp
+    mkdir /var/tmp
+    mount --bind /mnt/$PARTNAME/var/tmp /var/tmp
+
     mkdir -p /mnt/$PARTNAME/var/lib/kubelet
     mkdir /var/lib/kubelet
     mount --bind /mnt/$PARTNAME/var/lib/kubelet /var/lib/kubelet