HAMMER Utilities: Sync with 60E

HAMMER Utilities: Sync with 60E

* Change the cycle file to hold an entire B-Tree base key, plus an optional
  TID (used by the mirroring code).

* Flesh out the mirroring code.  Add timeout (-t) support.  Add cycle file
  support.

* When mirror-copy is used have the target sync the filesystem
  and acknowledge completion and store the completed TID in the cycle
  file.

* Incremental mirroring now works when using mirror-copy with a cycle file.

* Add mirror-dump, aka hammer mirror-read ... | hammer mirror-dump, for
  debugging.