img_check.sh: FAIL if motd matches DigitalOcean's motd from LAMP or LEMP

[jgannondo]

On occasion we see that a Vendor builds their app on top of our LAMP or LEMP app, but then doesn't change the MOTD.

In those cases, the motd will read something like:

Welcome to DigitalOcean's 1-Click LEMP Droplet.
To keep this Droplet secure, the UFW firewall is enabled.
All ports are BLOCKED except 22 (SSH), 80 (HTTP), and 443 (HTTPS).

In a web browser, you can view:
  * The LEMP 1-Click Quickstart guide: https://do.co/2GOFe5J#start
  * Your LEMP website: http://134.209.221.37

On the server:
  * The default web root is located at /var/www/html
  * The MySQL root password is saved in /root/.digitalocean_password
  * Certbot is preinstalled. Run it to configure HTTPS. See
    https://do.co/2GOFe5J#enable-https for more detail.

For help and more information, visit https://do.co/2GOFe5J

even though this is not the DigitalOcean LEMP app.

To resolve this issue, it may be sufficient to modify the script to check for:
Welcome to DigitalOcean's 1-Click LEMP (or similar) in the MOTD and emit a FAIL in that case.