ttcn3-pgw-test: make the testsuite dir writable by all users
When running jenkins.sh as root or any other user with UID different than UID=1000 of the 'osmocom' user we have in open5gs-{master,latest} images, programs spawned by osmo-uecups-daemon (e.g. ping) may fail to start. In such cases, osmo-uecups-daemon reports unexpected program termination with exit code=512. This is happening because the stdout and stderr of a spawned program are being redirected to "$VOL_BASE_DIR/pgw-tester/TESTCASE.prog.std{out,err}", for which the 'osmocom' user needs to have write permissions.
