Both copies refused to run unless /usr/sbin/tcpdump existed. Debian and Ubuntu
install it as /usr/bin/tcpdump, so the rogue DHCP detector never ran there and
the probe reported its tcpdump check as failed.
Resolve tcpdump through PATH and the standard system directories with
CommandUtils::find_executable, run the resolved path, and match that path when
the capture process is killed at the end.
Vinícius Ferrão
Mark Gurevich
GONG Jie
hu-weihua
XuWei