Add 'inode64' xfs mount option

Always put inodes next to their data to reduce disk seeks.

See http://xfs.org/index.php/XFS_FAQ#Q:_What_is_the_inode64_mount_option_for.3F
Add "logbsize=256k,delaylog" xfs mount options

Since we put the journal directly onto OSD data disks, avoid journal IO
as much as possible. See
http://xfs.org/index.php/XFS_FAQ#Q:_I_want_to_tune_my_XFS_filesystems_for_.3Csomething.3E
Merge pull request #28 from saschpe/release/stoney/master-xfs-tune

xfs tune