Fix launch_static_server script when only HTTP is wanted

We have "performance" tests which allow to ensure that we're not having
what we could call "performance regressions", such as a higher delay to
have a content loaded from a `loadVideo` call.

I wanted to run them yesterday for #1607, but they hanged indefinitely.

Turns out that our static server script, that we use here just to host
and serve our testing scripts returned a promise that was never resolved.

_(Note: we don't rely on external test runners nor on test frameworks
for our performance tests, we manually detect and launch local
chrome + firefox binaries on a local server serving our bundled
scripts (themselves importing the RxPlayer), and at runtime those
scripts send results to another "result" server when they're done)_

It was never resolved because we never properly handled the case in that
script were we wanted to launch an HTTP server but not an HTTPS one for
the same resource(s). This is now fixed.

Hopeful that performance tests now work correctly, it's been a long time
since I last ran them.

scripts/launch_static_server.mjs

@@ -74,6 +74,7 @@ export default function launchStaticServer(path, config) {
     httpServer.listen(config.httpPort, onHttpConnection);
 
     if (!shouldStartHttps) {
+      httpsServerStatus = "disabled";
       return;
     }
 
@@ -124,7 +125,7 @@ export default function launchStaticServer(path, config) {
         httpServerStatus = "error";
         if (httpsServerStatus === "success") {
           res({ http: false, https: true });
-        } else if (httpsServerStatus === "error") {
+        } else if (httpsServerStatus === "error" || httpsServerStatus === "disabled") {
           rej(err);
         }
         httpServer.close();