Changes

make/Makefile: update DISTRO, UPSTREAM_DISTRO

Update the Makefile, so it does not pick the wrong base distribution
when running make in e.g. osmo-bsc-master directly (without going
through ttcn3-*/jenkins.sh as jenkins does).

Change-Id: I31b2a1b8c70b973f4ec0f93d6e9e5e417afec994