Camera2: Don't set repeating request while testing digital zoom

Especially when we do capture-wait-checkresult pattern, there will lots of
repeating requests flooding in with different crop region, then end up with
fluctuating digital zoom, which is really not the design intention of this test.

Also make the test run faster by doing below:
- Reduce the number of zoom steps.
- Only test the largest size for different aspect ratios for digital zoom
combination test.

Bug: 16963565
Change-Id: Ib9abaf2418ec59d67f91f34a23950500dafefabd