Agent: Fix powershell second hop authentication

On the second hop powershell is trying to authenticate with
only a dummy username and passsword which is not enough.
We need to provide the local domain for the username,
which case is '.\'

monkey/infection_monkey/exploit/powershell.py

@@ -115,7 +115,7 @@ class PowerShellExploiter(HostExploiter):
 
     def _try_ssl_login(self, use_ssl: bool):
         credentials = Credentials(
-            username="dummy_username",
+            username=".\\dummy_username",
             secret="dummy_password",
             secret_type=SecretType.PASSWORD,
         )