[yocto] Add cmd.py library for python-core package

[Piotr Piwko]

Hi,

I would like to add cmd.py library to my final image. In order to do
so I modified python2-manifest.json file from poky delivery.

This solution works fine. However, is there any possibility to do not
change the global poky/python2-manifest,json file and get the same
result? I would like to provide this library only for particular image
not for all my supported ones. I tried to put new manifest file in
upper layers of my meta, but it seems to not be taken into
consideration by python recipe.

Thanks in advance for help.

-- 
Piotr Piwko
http://www.embedded-engineering.pl/