Inherited CollisionShape2D ignoring the Shape2D

[henriiquecampos]

Operating system or device, Godot version, GPU Model and driver (if graphics related):
Windows 10 Godot 2.1.3

Issue description:
When inheriting a scene with a CollisionShape2D node, the inherited scene doesn't overwrite the parent's shape. It should since it is an inherited scene and that's what inheritance is aimed for :P

Steps to reproduce:

1. Create a test scene with a StaticBody2D as ground for testing purposes
2. Create any physics character (RigidBody2D or Kinematicbody2D)
3. Add a CollisionShape2D to it, do not create a Shape2D yet
4. Create an inherited scene using the above scene as parent
5. Now Add a Shape2D to this scene
6. Instantiate it in the test scene with the ground
7. Apply a movement so it can collide with the ground

Watch it passing by the ground.

Now repeat the same process starting in the 3rd step, but now add a Shape2D to the parent scene

Test it again and now it collides.

I couldn't fix this even when I try to manually add the Shape2D using GDScript.

[bojidar-bg]

Duplicate of #2314 (same problem causing it), which was fixed in 3.0.