riotctrl_ctrl: one more indirection to get native

Since the native process is a child process of pyterm when called via
make we need to dig deeper for riotctrl. This also means that we require
pyserial to execute it.

dist/pythonlibs/riotctrl_ctrl/native.py

@@ -27,5 +27,6 @@ class NativeRIOTCtrl(riotctrl.ctrl.RIOTCtrl):
     def start_term(self, *args, **kwargs):
         super().start_term(*args, **kwargs)
         for child in psutil.Process(pid=self._term_pid()).children():
-            if self._set_debug_adapter_id(child):
-                break
+            for grandchild in child.children():
+                if self._set_debug_adapter_id(grandchild):
+                    break

dist/pythonlibs/riotctrl_ctrl/requirements.txt

@@ -1,2 +1,3 @@
 psutil
+pyserial
 riotctrl