Add Testsuite for Joomla

[J0WI]

Fix joomla-docker/docker-joomla#47

[samantha-again]

Typically I advise against using random variables in unit tests - you want them to be perfectly replicable on each run

[tianon]

In these tests, we encourage random variance because it usually increases the chances that the test is actually testing something meaningful instead of just hitting the happy path every time (for example, putting a "default" value in the test that just happens to work because it matches the default of the image when the image wouldn't handle a non-default value, for example).

[LaurentGoderre]

Since most of the test have the same setup logic, it might be desirable to convert them to use bash functions with parameters for the varying parts