Refactor: scheduler: make action UUID remapping easier to follow

Rename convert_non_atomic_uuid() to action_uuid_for_ordering(), add a doxygen
block, improve comments, rename variables, and simplify to make it easier to
follow.

This drops the free_original argument which was always FALSE, and moves the
notification check from rsc_expand_action() to action_uuid_for_ordering() which
allows the allow_notify argument to be dropped as well.

rsc_expand_action now calls action_uuid_for_ordering() only if the original
UUID is not NULL, which allows the return value to be guaranteed non-NULL.
It will now assert on memory allocation failures.

This also drops a redundant trace message so the remapping is only logged once.