tests: fix h3 server check and parallel instances

- fix check for availability of nghttpx server
- add `tcp` frontend config for same port as quic, as
  without this, port 3000 is bound which clashes for parallel
  testing

Closes #11553

tests/http3-server.pl

@@ -34,7 +34,7 @@ my $logdir = "log";
 my $pidfile = "$logdir/nghttpx.pid";
 my $logfile = "$logdir/http3.log";
 my $nghttpx = "nghttpx";
-my $listenport = 9015;
+my $listenport = 9017;
 my $connect = "127.0.0.1,8990";
 my $cert = "Server-localhost-sv";
 my $conf = "nghttpx.conf";
@@ -108,6 +108,7 @@ $certfile = abs_path($certfile);
 $keyfile = abs_path($keyfile);
 
 my $cmdline="$nghttpx --http2-proxy --backend=$connect ".
+    "--frontend=\"*,$listenport\" ".
     "--frontend=\"*,$listenport;quic\" ".
     "--log-level=INFO ".
     "--pid-file=$pidfile ".

tests/runtests.pl

@@ -314,7 +314,7 @@ if (!$ENV{"NGHTTPX"}) {
     $ENV{"NGHTTPX"} = checktestcmd("nghttpx");
 }
 if ($ENV{"NGHTTPX"}) {
-    my $nghttpx_version=join(' ', `"$ENV{'NGHTTPX'} -v 2>/dev/null"`);
+    my $nghttpx_version=join(' ', `"$ENV{'NGHTTPX'}" -v 2>/dev/null`);
     $nghttpx_h3 = $nghttpx_version =~ /nghttp3\//;
     chomp $nghttpx_h3;
 }