Improve phpunit configuration 2.x

[alexislefebvre]

Cherry-picks from #8

[alexislefebvre]

It looks like tests are failing randomly because sometimes the cache has been populated before running the tests that depend on them.

It could be sure by deleting the cache of fixtures before running the tests (dirty) or avoiding collision in caches (clean).

[alexislefebvre]

The tests that rely on users ids are fragile, they should be updated. For example: fetch user by email instead of id.

[alexislefebvre]

TODO: check that the issue is not how private static $cachedMetadatas = []; is populated or not emptied when it should, see calls to

LiipTestFixturesBundle/src/Services/DatabaseTools/AbstractDatabaseTool.php

Line 83 in 9ec9d52

private static $cachedMetadatas = [];