Bookie disk monitor should also monitor journal disks

[sijie]

FEATURE REQUEST

1. Please describe the feature you are requesting.

currently we monitor ledger and index directories. we should also monitor journal directories and turn bookies into readonly when journal disks are full.

2. Indicate the importance of this issue to you (blocker, must-have, should-have, nice-to-have). Are you currently using any workarounds to address this issue?

should-have

3. Provide any additional detail on your proposed use case for this feature.

a simple approach is just adding another ledger dirs manager/monitor to monitor journal directories. However this approach might not work well, because there will be 2-3 ledger listeners on reacting to different disks. they are acting independently so there will be a lot of race conditions on handling state transition.

a better approach is to refactor the ledger dirs manager and monitor to have one manager and monitor react to state transaction.