Property `RetryAcquireTrait::$retryDelay` sets the minimum delay, but not the exact delay. In fact, the delay may be longer. Because of this, sometimes less than 20 blocking attempts occur. Checking the exact number of locks sometimes leads to the following errors:
```
$ vendor/bin/phpunit --filter=testRetryAcquire
PHPUnit 4.8.34 by Sebastian Bergmann and contributors.
F
You should really fix these slow tests (>500ms)...
1. 1050ms to run yiiunit\framework\mutex\RetryAcquireTraitTest:testRetryAcquire
Time: 4.08 seconds, Memory: 44.00MB
There was 1 failure:
1) yiiunit\framework\mutex\RetryAcquireTraitTest::testRetryAcquire
Failed asserting that 19 is identical to 20.
/yii2/tests/framework/mutex/RetryAcquireTraitTest.php:36
/yii2/vendor/phpunit/phpunit/phpunit:52
FAILURES!
Tests: 1, Assertions: 3, Failures: 1.
```
I reworked the test so that it checks the duration of the delays, but not the exact number of blocking attempts.
- Increase frequency of lock tries for `yii\mutex\FileMutex::acquireLock()` when $timeout is provided (rob006)
- Add support for `$timeout` in `yii\mutex\PgsqlMutex::acquire()`
