Wait for Plesk initialization before tests execution

Getting disk usage details (plesk#54)

Getting disk usage details functionality added

Merge pull request plesk#52 from mrsombre/fix-test-webspace

Fix test creating webspace with disabled PHP handler

Merge pull request plesk#50 from mrsombre/fix-win-tests-2

Fix tests for running on Windows host Part 2

Merge pull request plesk#47 from mrsombre/tech-dbarsukov-maintenance

Update composer.json, removed composer.lock

Update composer.lock

Merge pull request plesk#40 from plesk/upgrade-phpunit

Upgrade PHPUnit 7.x, PHP 7.2 and Plesk 17.8