Changes

testenv: add --install-package

Add an option to quickly install packages in the container. This is
useful when making a new SUT run with osmo-ttcn3-hacks and figuring out
which packages need to be installed to make the build pass (without
rebuilding the whole container for each missing dependency). It can also
be used to quickly install additional debugging tools (strace, valgrind,
etc.). A cache for the deb files is already getting mounted inside the
container.

Change-Id: Ie54817e6c0334a224a612521beb378537c10d39d

sgsn/SGSN_Tests_SNS.cfg: adjust to recent changes

Fix this error:
  Error: Error message was received from HC at 10.0.2.100 [10.0.2.100]: Error while setting parameter field 'SGSN_Tests.mp_ranap_cfg[0].sctp_addr' to '{ 23908, "127.0.0.103", 2905, "127.0.0.200" }': Non existent field name in type @RAN_Adapter.RAN_Configuration: sctp_addr

Fixes: 0cdd73a8 ("Split SCCP_Adapter out of RAN_Adapter")
Change-Id: I62a1188aa3346fda3f0674296629ade51a02088f

testenv: set PYTHONUNBUFFERED=1

Prepare to run PyHSS, which needs this variable to be set or else no log
messages are printed. This problem exists with potentially all python
scripts that testenv would run, so set the env var for all commands.

Change-Id: I155f7c7bd9b985094e36fee6c6a2acfe556f580d

hlr: add HLR_IMPL_PYHSS

Prepare to run the HLR testsuite against PyHSS.

Related: OS#6862
Change-Id: I0989374d777aabf5afaf224faeb0cb2ff4e603e6

hlr: don't test OsmoHLR-only features with PyHSS

Proxy, mslookup and creating subscriber on demand are not implemented in
PyHSS, so don't test these features when testing PyHSS.

Related: OS#6862
Change-Id: I0c4905dd3f73abfe9f7cc77fc045368b9499aade

hlr: add MSC to ccm_pars.name

Fix an immediate disconnect from pyHSS:
  [ERROR] 127.0.0.1:9999: Role not found in tags. 'sgsn' or 'msc' must appear in one of there tags: TYPE, UNIT, UNITNAME. Closing connection.

Related: OS#6862
Change-Id: I1813e49ec286892c1a637deb99908903613696aa