Changes

hlr: testenv: fix running pyhss from debian pkg

Move the run_in_venv.sh script that is only used by pyhss from the
generic location _testenv/data/scripts/run_in_venv.sh to
hlr/pyhss/run_in_venv.sh and hardcode the path
/opt/venvs/pyhss/bin/activate in there when running from binary
packages. This is the path used in the binary package in the Osmocom
OBS, the default path from dh_virtualenv. The package doesn't install
pyhss_gsup etc. to /usr/bin, as these are usually not meant to be
directly started without the systemd services that have the
/opt/venvs/pyhss path hardcoded.

Also put 'export PYHSS_CONFIG=config.yaml' in there, now that
the script is pyhss specific.

Related: https://dh-virtualenv.readthedocs.io/en/1.2.1/usage.html
Change-Id: I0cdf1a9f220ddd2ef0866d0d11d1e3f6056a1cba