ttcn3-docker-run.sh: Fix dumpcap failing to access /data inside docker
In docker, the /data dir is mapped to $VOL_BASE_DIR, which is created by docker-playground.git jenkins-common.sh, hence as the user running jenkins.sh in the host system. As a result, when the dir is mapped to /data, inside the container it will have the UID:GID of the outter user, not the one inside docker.
Before this patch, if a ttcn3 container was started in jenkins.sh with --cap-add=NET_ADMIN, then osmo-ttcn3-hacks.git/ttcn3-tcpdump-start.sh would select dumpcap instead of tcpdump, to attempt to record a pcap file to /data/$testcase.pcap. Due to some unknown way of dropping privileges done by dumpcap though, it was unable to open the /data/$testcase.pcap due to /data being owned to another user (tcpdump doesn't have this problem).
This patch fixes the above scenario by making sure /data is chowned to the user running stuff inside docker. This is already kinda expected since there's a fix_perms() script in jenkins-common.sh reverting files created during the test so that they can be accessible by outter user once everything is finished.
