tests: add distlib to requirements.

* This may not be needed for tests but it's required for dev environment
  for quads-server so adding it here.

Change-Id: I7c21c435ee1c08261a0bb0c3756a0f235694ea36

requirements.txt

@@ -28,3 +28,4 @@ paramiko>=3.0.0
 argcomplete>=3.1.2
 requests>=2.31.0
 validators>=0.20.0
+distlib>=0.2