Drush make options for Drupal plugin broken with new Docker images

[joeparsons]

After updating our Drupal 7 Probo config to use the new supported Docker images (for https://blog.probo.ci/probo-1404-and-1604-images-removed-security), our existing drush make based configuration no longer works and these errors can be seen in the ProboCI console (even after adding drupalVersion: 7 to our config):

$ drush make build-ua_quickstart.make.yml /var/www/html --no-cache
bash: line 7: drush: command not found
$ rsync -a /src/ /var/www/html/profiles/ua_quickstart
bash: line 8: rsync: command not found

At least part of the problem seems to be that the drush symlinks that was recently added in #187 are created until the addScriptAppendSettingsPHPSettings() step in the populateScriptArray() method of the Drupal.js Probo plugin which is after the addScriptRunMakeFile() step is run.

I have no idea why the rsync: command not found bash error is happening.