use certbot-auto --non-interactive flag

Hi,
Many thanks for your work.

While using the `cert-renewal-haproxy.sh` with cron as root, I experienced an issue with dependancies the certbot-auto bootstraper was trying to update, using interactive mode.

Cerbot-auto bootstrap was calling apt-get install without the default _yes_ flag, thus the script was aborting, as apt-get was not receiving `y` to continue.

Using the --non-interactive flag in the `issuecert` shortcut function allows to force the bootstraper using default yes flag (`-y`) with apt-get.

Start in cert-renewal-haproxy.sh and locate the issuecert shortcut function. Check how it invokes certbot-auto, then verify that the renewal path can run from cron without an interactive apt-get prompt. Done means the command uses the requested non-interactive behavior.

Written by the indexing model from the issue text.