Tests: create process group when running daemons.

This allows to run daemons indirectly (e.g. via shell) and still be able
to kill them without external pid file.

lib/Test/Nginx.pm

diff --git a/lib/Test/Nginx.pm b/lib/Test/Nginx.pm
index 1e2884a..c2a5aee 100644
--- a/lib/Test/Nginx.pm
+++ b/lib/Test/Nginx.pm
@@ -114,7 +114,8 @@
 
 	while ($self->{_daemons} && scalar @{$self->{_daemons}}) {
 		my $p = shift @{$self->{_daemons}};
-		kill 'TERM', $p;
+		# SIGTERM to process group
+		kill -15, $p;
 		wait;
 	}
 
@@ -154,6 +155,7 @@
 	die "Can't fork daemon: $!\n" unless defined $pid;
 
 	if ($pid == 0) {
+		setpgrp(0, 0);
 		if (ref($code) eq 'CODE') {
 			$code->(@args);
 			exit 0;