test: fix testcpg build on FreeBSD9
HOST_NAME_MAX is intentionally NOT defined on BSD.
Users of HOST_NAME_MAX should be using sysconf or use very
conservative values.
limits.h still defines _POSIX_HOST_NAME_MAX. use that instead.
Signed-off-by: Fabio M. Di Nitto <fdinitto@redhat.com>
Reviewed-by: Jan Friesse <jfriesse@redhat.com>