An element can define a list of elements provided by itself. This allows
using an alternative element and keeping element dependencies at the
same time. This will be needed for example for mariadb element which will be
an alternative to mysql element - mysql dependency can be kept everywhere
but user can choose mariadb explicitly as a replacement by putting "mysql"
into "element-provides" file.
Change-Id: I7f193612f279dd71d9f1f1edfc60009838a00c5a
This commit refactors the python code in diskimage_builder slightly. This is
in preparation for a larger review that adds more functionality to the python
code, namely the ability to apply elements to the current system as opposed to
a chroot. Further, the refactorings can stand on their own for better clarity.
They include:
- renaming elements.py to element_dependencies.py. Adds clarity about the
purpose of this module.
- updating other code for this rename.
- move tests into a tests submodule.
Change-Id: I5519cc52398e442b24e33802bae42070d64b0c1d
