Description
To help the work on the redofs (HBASE-14090) we need some rework on the "filesystem" interfaces.
This task just moves the WAL related things out of MasterFileSystem.
This task is not meant to create a good interface for the wal but just to move out things from MasterFileSystem to be able to start working on that. the fixup of the wal interface will be done later in another jira.