The Cooker class is too large and needs to be split up into different
functional units. Splitting out the collections code into its own class
seems like a good place to start to try and disentangle things.
(Bitbake rev: ca1fcbb6e214c155a05328779d3d326e10c5eac0)
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>