BSC_Tests: split up f_mt_call and f_mo_call

The functions f_mt_call and f_mo_call establish a call, hold it
for 3 sec. and tear it down again. However, there may be test
situation where one wants to establish a call and then hold it
in order to perform other actions.

- split up the function into an _establish and _hangup part.
- add a replacement f_mt_call and f_mo_call function for the
  already existing testcases

Change-Id: I0da9cf64d10de4036eb037ef5e491bfe3088670b
1 file changed