Maybe fix flaky testDetachCalledWhenDestroyFragment

The activity.isDestroyed() flag might be toggled before
fragment gets destroyed, changed test to wait fragment
being destroyed.

Bug: 35462054
Test: testDetachCalledWhenDestroyFragment
Change-Id: Ib6b666a8dd8becdd7e4312dfe6dc2020862ace9f
6 files changed