Avoid tainting too many nodes if their deletion breaches ASG min

[bianchi2]

Problem

It is possible that escalator hits terminating nodes will breach minimum node size condition which prevents it from scaling down/deleting nodes in the nodegroup. This results in empty nodes running for no reason until ASG_DESIRED - NODES_TO_TERMINATE >= ASG_MIN (ie some manual intervention may be required)

Proposed Solution

While this situation can be caused mostly by bad timing and specific escalator configuration (increasing the time until a node would get deleted), it would be good to do some maths before tainting nodes, namely checking if ASG_DESIRED - NODES_TO_DELTE < ASG_MIN in other words run the same check as in DeleteNodes function but before nodes are tainted/marked for removal.

[vincentportella]

lgtm