Fixed the CacheCheck causing race conditions in some cases

[jonnyka]

If you have multiple environments, like subdeployments, and you run the CacheCheck, it can cause race conditions, because multiple environments write / read the same cache key (laravel-health:check).

By adding the random string from the test cache value to the key itself, we can avoid that race condition.

Also added Cache->forget(), so we don't flood the cache with all those randomized keys.

[freekmurze]

Thanks!