Add additional env vars for drupal

[joecorall]

Without this, install_default was failing on new site installs with

$ source /etc/islandora/utilities.sh
$ install_site default
--driver
--host
--port
--dbuser drupal_default
--dbname drupal_default
PROFILE: minimal
[email protected]
--account-name=admin
[email protected]
--locale=en
--site-name=Islandora Digital Collections
--sites-subdir=default
USE_EXISTIG_CONFIG: --existing-config
EVERYTHING ELSE:
Missing one of required options: --host --port --db-user --db-password --db-name

May be best fixed at the image: Islandora-Devops/isle-buildkit#351

[joecorall]

Hmm this isn't it - there's something about cloning the starter site and running the install once that makes the second attempt succeed.