blk/kernel: use open file description lock if available

blk/kernel: use open file description lock if available

* use OFD lock if available. OFD is Linux specific, and only available
  on 3.15 kernels. OFD is able to synchronize both threads and
  processes. and has simpler semantics. this is just a cleanup.
  as we don't create threads for acquiring the flock.
* use BSD flock(2) as a fallback
* return the errno right away, without printing logging messages.
  for two reasons:
  - writing logging messages would reset the errno.
  - the caller of _lock() also prints the logging messages along
    with strerror(errno)

Fixes: https://tracker.ceph.com/issues/46124
Signed-off-by: Kefu Chai <kchai@redhat.com>