propagating the "unlock" lock type through this high-level api is
nonsense. it doesn't make sense to treat locking and unlocking as
similar operations; unlocking *must* not not interruptible by our
checkInterrupt machinery or it will just leave locks lying around
for a potentially very long time. unlock operations should not be
taking long enough to *want* them interrupted anyway. even on nfs
this makes very little sense because nfs waits *uninterruptibly*.
Change-Id: I10d605c8fe6c651bee64466eee1f8e20251d39f4
(cherry picked from commit aa87c8aa93)
