system-traffic: use appropriate nc options for installed version

system-traffic: use appropriate nc options for installed version

Test cases using netcat ("ICMP related" and "ICMP related with NAT")
currently fail on systems using the nmap version of nc because this
version does not support the -q command-line option.

Fix this by detecting which version of netcat is is in use and
using the "--send-only" command-line option when the nmap flavor
is detected, and using "-q 1" otherwise (openbsd and traditional
versions).

Tested via "make check-kernel" on RHEL7 (nmap version of nc),
Debian 8.2 (openbsd version of nc), and Ubuntu 14.04 ("traditional" nc).

Signed-off-by: Lance Richardson <lrichard@redhat.com>
Signed-off-by: Joe Stringer <joe@ovn.org>