Docker: Fix PHP tests

[Abijeet]

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:
sebastianbergmann/phpunit#2353 for more
information.

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

[ssddanbrown]

Thanks for this @Abijeet.

I really don't want to have to alter an app files just to suit the docker setup unless absolutely required, Especially those changes in phpunit.xml as I'm sure I'll end up spending time in the future trying to understand the difference in variables or I'll get caught out when trying to override them in testing.

The mysql_testing database connection takes a TEST_DATABASE_URL env option, This should take priority over other options and takes the format of mysql://user:password@host/table so that could be used if needed.

With this, test database migration is done automatically during init but seeding is done manually via command. I think it'd be better, and consistent with the non-docker flow, if both of these were done manually. Auto migrating alongside the non-test DB could cause confusion if errors are thrown and will slow down start-up and increase the output.

[ssddanbrown]

Thanks again @Abijeet.

I made the changes advised above within commit 43c2fc3.