Remove stray files (probes or lock files) created by background threads

Remove stray files (probes or lock files) created by background threads

NOTE: port back from master branch.

On process exit, it was possible that the filesystem timestamp
resolution measurement left behind .probe files or even a lock file
for the jgit.config.

Ensure the SAVE_RUNNER is shut down when the process exits (via
System.exit() or otherwise). Move lf.lock() into the try-finally
block when saving the config file.

Delete .probe files on JVM shutdown -- they are created in daemon
threads that may terminate abruptly, not executing the "finally"
clause that normally removes these files.

Bug: 579445
Change-Id: Iaee2301eb14e6201406398a90228ad10cfea6098