Set admin password during install

[GeorgianaElena]

Added the option to set the admin user password during install (closes #263).

If the installer is called with --password option, then a password will be requested for each admin user specified with --admin*. If --password is not present, the script will behave like before.

@yuvipanda, can you please give me some advice about how/if should I test this? 👀

[GeorgianaElena]

@yuvipanda, according to the docs, in order to add multiple admins during install there should be something like: --admin a1 --admin a2.
This didn't work for me (it only stored the last one). Doing instead --admin a1 a2 works.
From argparse's docs it looks like there should be an action="append" in order to be able to use --admin multiple times.

[yuvipanda]

w00t, thanks for working on this, @GeorgianaElena!

1. I think we should ask users for passwords in the form '--admin username:password --admin username:password', so we can match usernames to passwords easily. This re-uses how HTTP does basic auth usernames / passwords for syntax...
2. whoops re: append. Would love a PR for that.

What do you think?

[GeorgianaElena]

Thanks for the feedback @yuvipanda :D
I will open a PR to add the append.
I chose not to have --admin:password because I feared that the password will be stored along with the install command in bash history and I think it is also visible when doing ps while the script is running.
But I totally agree it is not ideal to have the installer request user input and if the concern above is not applicable here, I'm more then happy to have it as you suggested.

[GeorgianaElena]

@yuvipanda, I've addressed your feedback, added tests and updated the docs. Let me know what you think :)