start implementing the TC_paging() PCU test

Implement a basic paging test for the PCU, which is passing for paging
via TMSI (but only if osmo-pcu is started after the test is started).

Previously, this test code amounted to a debugging loop which
never terminated.

Change-Id: Id0384e0742ab91983615e4f1c883bb044c1c8b18
Related: OS#2404
3 files changed