- fix an issue of turning off tcpdump
- tcpdump usage is moved to
src/softwaresupport/multi_server_functions.pyand also integrated insrc/srv_msg.pyas test step - by default tcpdump will filter out everything except dhcp and dns ports
- port filters can be defined by user
- now it can also automatically start on remote server (and download pcap to results directory) but I consider it as debug tool so it's disabled by default
fix was tested in https://jenkins.aws.isc.org/view/Kea-manual/job/kea-manual/job/tarball-system-tests/149/ and https://jenkins.aws.isc.org/view/Kea-manual/job/kea-manual/job/pkg-system-tests/69/