CA-142045: Buttons are truncated on Workload Balancing Configuration for New Pool wizard.

Fix the display issues when WLB Configuration Dialog size is changing:
1. OK and Cancel buttons are truncated.
2. OK and Cancel buttons do not keep at the bottom/right corner of the dialog.
3. The height of the SplitContainer does not track the change of the height of the dialog.

Signed-off-by: Hui Zhang <hui.zhang@citrix.com>