Fix the bookie doesn't transition to writable

[zymap]

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Motivation

When bookie started with readonly, and the disk usage is smaller than the warning threshold, it won't transition to write mode. Notify the disk writable when init the bookie

[zymap]

For the first case, I think if you start bookie with readonly, the bookie will in forceReadonly and won't be writable anymore. So even if the disk has space and it won't transition to the write mode.

For the third case, yes. It is very difficult to know if it is controlled by the rest API or the disk threshold for now. So if you want to make bookie into readonly forever, you need to make it to the forceReadonly, not the readonly state. So i think it should be acceptable?

[mattisonchao]

Do we need safe run here?