handover_test: add test_balance_congestion_by_percentage.ho_vty

Considering feedback by a customer, we prefer congestion balancing by
using percentage of overload instead of number of lchans of overload.
This test is intended to illustrate the change in behavior.

Change-Id: I314915718f66aec50e8dcf94569b0a52ca34b96f
2 files changed