Use an ephemeral port in test runs to avoid 'bind: address already in use'

psiphon/common/obfuscator/obfuscator_test.go

@@ -692,13 +692,13 @@ func obfuscatedSSHConnTestHelper(
 
 	keyword := prng.HexString(32)
 
-	serverAddress := "127.0.0.1:2222"
-
-	listener, err := net.Listen("tcp", serverAddress)
+	listener, err := net.Listen("tcp", "127.0.0.1:0")
 	if err != nil {
 		t.Fatalf("Listen failed: %s", err)
 	}
 
+	serverAddress := listener.Addr().String()
+
 	rsaKey, err := rsa.GenerateKey(rand.Reader, 2048)
 	if err != nil {
 		t.Fatalf("GenerateKey failed: %s", err)