Thanks so much for taking the time to go into detail. I just followed your advice and found that I could not replace the user name on the prompt, so I ran it to the end and modified the app.yml file to hold an empty string (“”) in that field.
Unfortunately, I could not verify that these setting would work for me because, when I tried to build it, the script complained that my Docker 1.7 was not sufficient, that I needed 1.8 or better. When I tried to update I was informed that my kernel was not 3.10 and I could not install the latest Docker. So I am off to figure out how to either get Docker 1.8, or manually install Discourse from packages & sources (shudder!) or get my hosting provider to upgrade my CentOS 6.8 to something newer, which may or may not work.
I really wish the “easy” instructions would include a link to the full requirements so that I could check them all off before even starting. This is like being fed ingredients one at a time and running to the store to buy item, only to have the next ingredient revealed once you try again! 
But that’s not your issue, thanks for this valuable info and I’ll test it in detail once I solve these other problems. Maybe I should jump into trying to do a full install from packages & source, etc.