* Add test_get_state_from_sibling_not_cached
A better unit test to catch issues with refetching parent states
and calculating the wrong parent state names to fetch.
* _determine_missing_parent_states: correctly generate state names
Prepend only the previous state name to the current relative_parent_state_name
instead of joining all of the previous state names together.
* [REF-2219] Avoid refetching states that are already cached
The already cached states may have unsaved changes which can be wiped out if
they are refetched from redis in the middle of handling an event.
If the root state already knows about one of the potentially missing states,
then use the instance that is already cached.
Fix#2851
55b0fb36e8