sysmocom: emergency_preemptive_call.py: Avoid test failure if 2nd call not fully established
It may happen that the non-emergency call MT leg is still not properly released when the emergency call MT leg is to be assigned a TCH, meaning BSC will fail with an Assignment Failure upon Assignment request from MSC. The test sometimes passed and sometimes didn't, due to above mentioned race condition. Let's relax a bit the test expectancies to have it always passing, while still verifying preemption happens, and MT phone is reached.
