Replace TestHTTPMockServer with python script

This seems to work fine in a `nix build`-sandbox as it doesn't depend on
`getprotobyname`.

t/jobs/server.py

@@ -0,0 +1,35 @@
+#!/usr/bin/env python3
+
+from http.server import BaseHTTPRequestHandler, HTTPServer
+from sys import argv
+
+
+def factory(file):
+    h = handler
+    h.file = file
+    return h
+
+
+class handler(BaseHTTPRequestHandler):
+    def do_POST(self):
+        self.send_response(200)
+        self.send_header('Content-type', 'application/json')
+        with open(self.file, 'w+') as f:
+            f.write(f"{self.path}\n")
+            length = int(self.headers.get('content-length', 0))
+            body = str(self.rfile.read(length).decode("utf-8"))
+
+            f.write(f"{body}")
+        self.end_headers()
+
+        message = "{}"
+        self.wfile.write(bytes(message, "utf8"))
+
+
+if __name__ == '__main__':
+    try:
+        assert len(argv) > 1
+        with HTTPServer(('localhost', 8282), factory(argv[1])) as server:
+            server.serve_forever()
+    except KeyboardInterrupt:
+        pass