debian-stretch-titan/Dockerfile: install osmo-python-testsWe need osmo_interact_vty.py in order to obtain talloc reports foreach test case automatically. See [1] for more details.Change-Id: Ida8e08e7fe4f171f934a2d4eef4568da7c398f5cRelated: [1] I1b03b17426d8760c55976e3b78ca2f3af248c055