Raft engine should be able to recover/restart even if there is no disk space to write anything

[v01dstar]

If the header of the last log file is broken, and the there is no disk space, raft engine will not be able to start, because it requires rewriting the header during the recovery process. This can be avoided by deleting the last log file that has broken header. And, no space error will only kick in while there are new writes.