Fix permissions

This is a follow-up PR for #7, since https://github.com/rancher/local-path-provisioner/commit/3256bdf61b14c6b7e517ede0f56cfebeaf28e616, unfortunately, did not fully fix the issue.

The example I supplied is not ideal. It works with your fix because it uses Busybox which doesn't have group 1000 so the user runs with gid=0. I added `id` to the script which prints the following:

`uid=1000 gid=0(root) groups=0(root),1000`

Now, when I use an image that actually has a user with uid=1000, gid=1000, such as `jenkins/jenkins` it doesn't work because the user does not belong to group 0 in this case:

`uid=1000 gid=0(root) groups=0(root),1000`

This fixes the issue using `0777` as Minikube does.