[Improvement] Allow ITS to update crashed pods

## User Story
When a pod get crashed (such as OOMKilled), a user may want to update it (such as increase its memory limit). However, this is not possiable because ITS contoller only update a pod when it is ready and available.

requested by @wangyelei 

## Proposed solution
We may want to loose this constraint in ITS controller. The rolling update process still needs to be effective.