offline store need be considered in balance leader/region

[disksing]

When a store is not up, it is excluded from the leader/region balance. I think a better behavior  would be:

1. If the count(or size) of an offline store is below average, we can exclude it in balancers.
2. If the count(or size) of an offline store is above average, we should consider it in balancers.

[huachaohuang]

I think we can limit an offline store as a source store (but not a target store) in balancers.

[nolouch]

Maybe we can consider a new single fail-over balance, now checker couldn't found abnormal region immediately. and there are some priorities for scheduling the fail store regions. like hot region.

[disksing]

Yes we can. But I guess it's not related to this issue.