Low priority idles can fire more or less randomly, and consequently two
consequent runs of LibreOffice differ in the amount of the idles that have
been performed during an operation.

This commit adds a possibility to turn on a 'deterministic mode' where two
subsequent runs of LibreOffice trigger about the same amount of events when
they perform the same set of operations.

Change-Id: I92566ef4eee20e7d604cfd48f01c4df30c77e653