Comment 10 for bug 1153926

The issue being solved here is when a deleted flavor's info has to be shown in the instance details.

The deleted flavor might have been replaced with some other flavor with the same flavor id, hence while showing instance details, the api might fetch completely different flavor details since the flavor id matches.

To solve this, we can do
1) Always fetch flavor details from instance's system_metadata instead of flavor api

2) Fetch flavor details from instance's system_metadata only if the original flavor is marked as deleted or 404 when trying to fetch that old flavor (my current patch does this)

1st option doesnt break flavor api get status from 200 to 404, it doesnt touch the flavor api at all.
2nd option has to rely on flavor api not getting deleted flavors in the flavor get api call.