Tests: while starting nginx monitor pidfile instead of sleeping.

This reduces test execution time significantly.

lib/Test/Nginx.pm

diff --git a/lib/Test/Nginx.pm b/lib/Test/Nginx.pm
index 2c9ecf7..26f5624 100644
--- a/lib/Test/Nginx.pm
+++ b/lib/Test/Nginx.pm
@@ -97,7 +97,10 @@
 
 	# wait for nginx to start
 
-	sleep 1;
+	for (1 .. 30) {
+		select undef, undef, undef, 0.05;
+		last if -e "$self->{_testdir}/nginx.pid";
+	}
 
 	die "Can't start nginx" unless -e "$self->{_testdir}/nginx.pid";