os/FileStore: disable fadvise on XFS

fadvise(DONTNEED) on XFS can break writeback ordering and zeroing; see

      http://oss.sgi.com/archives/xfs/2013-06/msg00066.html

If we detect XFS, turn this option off.

Signed-off-by: Sage Weil <sage@inktank.com>
Reviewed-by: Samuel Just <sam.just@inktank.com>
ceph-disk: make list_partition behave with unusual device names

When you get device names like sdaa you do not want to mistakenly conclude that
sdaa is a partition of sda.  Use /sys/block/$device/$partition existence
instead.

Fixes: #5211
Backport: cuttlefish
Signed-off-by: Alexandre Maragone <alexandre.maragone@inktank.com>
Reviewed-by: Sage Weil <sage@inktank.com>
Merge remote-tracking branch 'gh/next'