Get rid of GridTestUtils.retryAssert method.

For now we have GridTestUtils.retryAssert() method which runs a closure 'n' times to check if some invariantes become ok, eventually.

This method catch assertion error (this looks like a very bad idea) and can print them to log many times even if assertion is acceptable for the moment.
Also, it is possible to miss an assertion is not related to those ones that closure checks  (e.g. assertion error thrown from ignite internals).

Let's replace retryAssert with GridTestUtils.waitForCondition() usage to make logs clearer and to avoid possible false positive results.