When all disks are full start Bookie in RO mode if RO mode is enabled
This will work only if "isForceGCAllowWhenNoSpace" is allowed, since LedgerDirsManager.getWritableLedgerDirsForNewLog will be able to find new writableLedgerDir even when all disks are full.
If bookie has died abruptly then it may have missed flushing EntryMemtable and
IndexInMemoryPageManager. So next time when it starts when disc is full
it fails to create index file and it shuts down. So Bookie should be able to create index file though it has reached the diskusagethreshold, while starting the Bookie in Readonly Mode. But ofcourse there should be some config to safeguard when disk usable space is so low.
New Feature
Minor
