Create non-docked stack with right bounds if docked stack exist

We previously created a new stack with a bounds of half the screen
instead of using whatever space is left by the docked stack.

Change also takes care of issue where the adjustment bounds was
slightly off for non-docked stack.

Bug: 24460346
Bug: 24501077
Change-Id: Ib7f6c62bdf9309ca8916527dbb206e3719a36d9e