Fix test for run of 'fix-permissions.sh' early in the ISLE build process

[Digital-Grinnell]

Issue description

In my 'local' builds of ISLE there are conditions that cause the fix-permissions.sh script to run and issue error messages early in the build process. I've confirmed through tests that these "errors" are innocuous, they do no apparent harm, and that they do NOT occur when building a 'demo' instance from a pristine copy of ISLE. However, they are annoying and should be corrected to not return a false-negative error message.

In my tests, when the condition is present I find that the apache container has a /var/www/html/sites directory, so the test wrapper around the fix-permissions.sh call returns TRUE; however, the /var/www/html directory is otherwise EMPTY, so there's no valid Drupal site available for the script to act on.

I believe the test to run the script should be something more like this:

## Fix permissions using the drupal fix-permissions script.
if [ "$(-f /var/www/html/index.php 2> /dev/null)" ]; then 
    # Fix site directory permissions

For an issue, describe steps to reproduce the issue

System setup (OS information, software versions, etc):

• In my case running OSX, any version.

Steps:

1. Clone https://github.com/Digital-Grinnell/dg-isle/tree/local
2. cd to the clone
3. docker-compose up

What's the expected result?

Errors like this...

...
[services.d] starting services
Running fix-permissions script...
[services.d] done.
*********************************************
* Error: Please provide a valid Drupal path. *
*********************************************
This script is used to fix permissions of a Drupal installation
you need to provide the following arguments:
  1) Path to your Drupal installation.
  2) Username of the user that you want to give files/directories ownership.
  3) HTTPD group name (defaults to www-data for Apache).
Usage: (sudo) bash fix-permissions.sh --drupal_path=PATH --drupal_user=USER --httpd_group=GROUP
Example: (sudo) bash fix-permissions.sh --drupal_path=/usr/local/apache2/htdocs --drupal_user=john --httpd_group=www-data
XDEBUG OFF
...

What's the actual result?

There's no Drupal root to set permissions against at this early point in the build, so the fix-permissions.sh script has NOTHING to act on. There is NO harm in running the script, but the "error" message is both annoying and misleading.