Extend QTRY_COMPARE and QTRY_VERIFY macros

We need to fix CI, one of the most common complains is that CI machines
are overloaded and some tests simply timeouts. This patch extends QTRY*
macros to gather statistics. Each time a QTRY* macro is used it is
waiting for the expression to be true by certain time (by default 5 sec)
Next, if it failed, it waits twice as much to prove that the expression
is not affected by CI machine slowness, then fails anyway.

Before the next major release, we should decide if this functionality
should be included, as it changes behavior slightly.
The following task should be kept open until the decision has been
made:

Task-number: QTBUG-36036

Change-Id: I7ab5070cb7eb7d96a7289dd7b2bebf91d93090e5
Reviewed-by: Jędrzej Nowacki <jedrzej.nowacki@digia.com>
Reviewed-by: Jan Arve Sæther <jan-arve.saether@digia.com>
Introduce a way of explicit selection of the platform theme

Introduce a way of explicit selection of the platform theme to be used,
either through a new environment variable - QT_QPA_PLATFORMTHEME, or by
the optional -platformtheme command line argument.

Task-number: QTBUG-30091
Change-Id: Ieaa96b52265c3e48d056af7e56e793d8531fd7b3
Reviewed-by: Shawn Rutledge <shawn.rutledge@digia.com>
Reviewed-by: Friedemann Kleint <Friedemann.Kleint@digia.com>
Reviewed-by: Paul Olav Tvete <paul.tvete@digia.com>