hlr: Port HLR tests to use GSUP_Emulation

Going via GSUP_Emulation (rather than using GSUP_CodecPort directly)
adds many benefits, such as:
* ability to have multiple transactions in parallel
* no silent discard/ignore of unexpected GSUP messages, like those
  for IMSIs we don't expect.

Change-Id: Id2ddd6b81c374ad6350b62fcc5442436757d66cd
2 files changed