improved matching algorithm

- handle growing matching area together with unchanged screenshots
- search whole area every 6 seconds
Very interesting comments. I will add some notes in the same order:

* In the initial version of this solution I observed that many of the needles have a match very close from the original position. However, this is not true in console test.
* This can be true, but depends on the value of the timeout. Usually we put excessive timeouts to some asserts, to make sure that there is not a TO when the machine is very busy with other QEMUs.  Also long timeouts are rare.
* Uhm, this is not true (I hope) since https://github.com/os-autoinst/os-autoinst/commit/566adbe3a1880cefe1cd9f4d38a9568f2d10c709

Maybe we can test how this patch behaves in openqa.o.o, but I see some random decisions: why 0.02 and not avoid the search? why make a full search every 6 iterations, instead of ... 8 or 10, or func($timeout)?

How much faster is in sleposbuilder3?