Motivation
Currently BLT always generates a random password for user 1. On local environments we want to be able to define a username and password so we don't have to reset it after every single setup or use drush uli to get into the site.

Proposed changes
Since site:install allows for the --account-pass option, if a password is given in the blt config files, use it.

Testing steps

1. apply this patch
2. without changing anything else, run blt setup:drupal:instal -y --no-interaction
3. confirm random user name and password
4. add drupal.account.pass to your blt.yml file (optionally define a drupal.account.name as well for an easier test).
5. re-run blt setup:drupal:instal -y --no-interaction
6. confirm admin name and password are set to your custom ones defined in step 4.