These new variables are a list of elements chosen for the build along
with their full paths. For Python elements, IMAGE_ELEMENT_YAML is a
YAML formatted list that can be easily parsed. For bash elements,
"get_image_element_array" will produce an associative-array of the
same (working around lack of array export in Bash).
This list is intended for consumption of elements who need to copy
files from other elements, such as pkg-map and svc-map. As discussed
in I2a29861c67de2d25c595cb35d850e92807d26ac6, this list has already
been pruned and had overrides processed, so it is safe to simply walk
over this list with no further processing.
Since we're presenting the element list in a couple of different ways,
we combine it all into the element-info script. It will output an
eval-able string that declares the appropriate variables.
I've added some inline documentation so they still appear in grep.
The documentation is updated with examples, and moved to a more
appropriate location as a sub-section of the element sytle guide.
To test this out, use the associative-array in generate_hooks, where
we can now find the element's directory without searching.
Change-Id: Ibbd07d082ec827441def2d3f6240df3efdc6eae3
