Make finding optional components quiet

* Quick is considered in src/CMakeLists.txt.
* QuickTest is only required by tests/auto/qml.
  Add check for QuickTest for this folder.

Pick-to: 6.11
Change-Id: Ica1810baaa954f47cfbf7bfefb2d3cc28c5a0894
Reviewed-by: Ulf Hermann <ulf.hermann@qt.io>
Reviewed-by: Alexandru Croitor <alexandru.croitor@qt.io>