Refine the Registry required "hash mod value"

[grecinto]

The hash mod value required by the Registry module needs to be persisted once, perhaps where SOP saves the "store list" (in stores' base folder path).

Then once defined, it has to be read by all succeeding SOP transactions and reused its value. Once specified, the Transaction options parameter for "hash mod value" will then be ignored and this value reused.

Hash Mod Value is a global value, that once defined, all stores & transactions will reuse that same value.

[grecinto]

Implemented something simple, that just persist the value of Registry Hash Mod Value to a file in home folder. And use this file during reinstate failed drives function (in_red_fs/manage_btree.go's ReinstateFailedDrives) call.