Revert "Re-enable mac tests"

This reverts commit cc811f77fc4f48fb696784f0a51042bb736d7071.

GUI tests were temporarily disabled on Mac in 8ed38c7 and cc811f7 meant
to re-enable them, but in fact removed the GUI tests on every platform.
There is still plenty of instability in the tests, so we will first
restore GUI tests on non-Mac platforms, and then we'll try to properly
re-enable them on Mac, step by step.

Change-Id: Ic8ac32386cc9e7c5ea3172751d74138e30fa0fdf
Reviewed-by: Jan Arve Sæther <jan-arve.saether@digia.com>
Reviewed-by: Lars Knoll <lars.knoll@digia.com>
Fix tst_qquickflickable::stopAtBounds()

Change-Id: I7a6cc8ddb4cb4559498b74839bde57d12a3d68fd
Reviewed-by: Lars Knoll <lars.knoll@digia.com>
Mark tst_qquickanimations as insignificant on MinGW

tst_qquickanimations::pathInterpolatorBackwardJump() keeps constantly
failing in the CI on Windows MinGW builds.

Task-number: QTBUG-29062
Change-Id: I69511f8a45e98061ceb9a0f6782cc57940af3ce4
Reviewed-by: Simon Hausmann <simon.hausmann@digia.com>