File permissions for SSL key should restrict group/other read access

[dirkcuys]

Any account with access to the NUC can access the SSL key contents.
It might apply to more than just the key, should /home/ubuntu be readable by anyone other than user/group ubuntu or root?

[dnk8n]

@dirkcuys Done.

To try, you can rerun the installation (it is tested to be idempotent).