Package test command fails if phpunit.xml file does not exist

[KarinaRashchynskaya]

Hello,

I would like to recommend a possible feature in terms of package:test --parallel command. I noticed that in your latest updates, you add an extra functionality in terms of caching which requires loading the proper phpunit.xml file (6fc0c47).

However, the code enforces the file's path, considering that by default it would be in the laravel's base path.
Although, there are external packages which extend your class and their configurations files (phpunit.xml) have different paths or maybe do not exist.

So, my suggestion is, to let others to overwrite the required file (if they want).
I was thinking a solution like this :

#273

The above, will help external packages, which extend the nunomaduro/collision, to keep execute package:test --parallel command on their own configuration options.

Thank you