Stabilise ListView and GridView tests

Stabilise ListView and GridView tests

Some tests need to wait for view to be updated before proceeding. This ensures
a polish is received before proceeding

    - before checking through child items after initial load
    - after changing content y

    unless some other QTRY_* is already doing the job.

Also fixed some tests that randomly failed for other reasons.

Task-number: QTBUG-22872 QTBUG-23605

Change-Id: I2d41bf09fae09b90fd3aadbd5349e991c3339761
Reviewed-by: Martin Jones <martin.jones@nokia.com>