[docs] Add admin workflow for recovering from disk failure
[docs] Add admin workflow for recovering from disk failure

I didn't document how to rebalance tablets onto the repaired tserver if
necessary, since the process is complicated and error prone, and we hope
to have a rebalancing tool in the future. These docs will quickly become
outdated when KUDU-616 is fixed, but I think it's worth it to document
since we frequently receive questions on the topic.

Change-Id: I6541bffc5e9546c523df610fd8c025dd05e403bf
Reviewed-on: http://gerrit.cloudera.org:8080/6606
Tested-by: Kudu Jenkins
Reviewed-by: Adar Dembo <866ca730bfc7f544e3ebce604ceeba4879f23df0@cloudera.com>
Reviewed-by: Andrew Wong <b68e4fdc6430321a6b47400732ff97d7ae91234e@cloudera.com>

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