ksck doesn't identify tablets that are evicted but still in config

As reported by a user on Slack, ksck can give you a wrong output such as:

  ca199fafca544df2a1b2a01be9d5266d (server1:7250): RUNNING [LEADER]
  a077957f627c4758ab5a989aca8a1ca8 (server2:7250): RUNNING
  5c09a555c205482b8131f15b2c249ec6 (server3:7250): bad state
    State:       NOT_STARTED
    Data state:  TABLET_DATA_TOMBSTONED
    Last status: Tablet initializing...

The problem is that server2 was already evicted out of the configuration (based on reading the logs) but it wasn't committed in the config (which contains server 1 and 3) since there's really only 1 server left out of 3.

Ideally ksck should try to see what each server thinks the configuration is and see if there's a difference from what's in the master. As it is, it looks like we're missing 1 replica but in reality this is a broken tablet.