Changes

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.

Change-Id: Icb6b30e618e290d974a919fef34c6b5cb7eeb648
Related: OS#5913