Recovery: monitor, logging and other admin-friendly improvements

* Improved monitor thread. Now it provides HTTP interface via python's standard library SimpleHTTPServer so admin can use `wget`/`curl`/`fetch` to remotely obtain recovery stats. Stat file now left on fs after recovery is finished, so admin can use it in post-mortem or local monitoring tools. Also removed some code duplication.
* Improved logging. Now we are mirroring screen log to auto-rotating log file, which is also left on fs after recovery is finished to aid sysadmin.
* Cleanup stale files on start in case previous recovery was interrupted in very rude way.
* Use separate temp directories for different recovery types by default.
* Try to create default recovery dir on start.