Tests: change http timeout to 5s, imap/pop3/smtp to 3s. Excessive testing shows it should be enough to don't trigger false positive test suite failures on slow machines. Drop custom timeouts as previously used by dav_chunked.t accordingly.

--- a/lib/Test/Nginx/IMAP.pm
+++ b/lib/Test/Nginx/IMAP.pm
@@ -42,7 +42,7 @@ sub read {
 	my ($self) = @_;
 	eval {
 		local $SIG{ALRM} = sub { die "timeout\n" };
-		alarm(2);
+		alarm(3);
 		while (<$self>) {
 			log_in($_);
 			# XXX