Fix split task position behavior when landscape

On nav bar 2/3 key mode and device landscape, the top task should
always opposite to nav bar, so top task location should be right
when seascape and left when landscape.

On gesture nav mode, because the nav bar always locate bottom so
keep it behavior.

Bug: 150990456
Test: Use each gesture mode and enter split mode then check it
Change-Id: Ia46f765c43c947350ee4970ea86aa9a0d707ad7d