Parameterise the sockdir with the UID of the user

The top level socket directory is now called XRDP_SOCKET_ROOT_PATH.
Below that are user-specific directories referred to with the
XRDP_SOCKET_PATH macro - this name is hard-coded into xorgxrdp and
the audio modules as an environment variable.

XRDP_SOCKET_PATH now looks like $XRDP_SOCKET_ROOT_PATH/<uid>

XRDP_SOCKET_PATH is only writeable by the user, and readable by the user
and the xrdp process.

sesman/tools/sesrun.c

@@ -460,7 +460,7 @@ handle_login_response(struct trans *t, int *server_closed)
     }
     else
     {
-        rv = scp_get_login_response(t, &login_result, server_closed);
+        rv = scp_get_login_response(t, &login_result, server_closed, NULL);
         if (rv == 0)
         {
             if (login_result != E_SCP_LOGIN_OK)