Write a line like 'Misc_Helpers.mp_osmo_repo := "nightly"' into the
TTCN-3 config file (e.g. BSC_Tests.cfg), before starting the testsuite.
This allows executing different code paths in the tests based on the
repository.
Related: OS#5327
Change-Id: Ic06532f7a67e59458652c5cf4c8f6fee8113e703