Docker: Fix PHP tests

This creates another mysql_testing database during db service setup

Replace server with env tags in phpunit.xml in order to force
override certain parameters when tests are run. See:
https://github.com/sebastianbergmann/phpunit/issues/2353 for more
information.

Rename primary developer Docker database from bookstack-test to
bookstack-dev. bookstack-test is used as the mysql_testing database

dev/docker/entrypoint.app.sh

@@ -10,6 +10,7 @@ else
     composer install
     wait-for-it db:3306 -t 45
     php artisan migrate --database=mysql
+    php artisan migrate --database=mysql_testing
     chown -R www-data:www-data storage
     exec apache2-foreground
 fi

dev/docker/init.db/01.sql

@@ -0,0 +1,5 @@
+# create test database
+CREATE DATABASE IF NOT EXISTS `bookstack-test`;
+
+# grant rights
+GRANT ALL PRIVILEGES ON `bookstack-test`.* TO 'bookstack-test'@'%';