LU-419 enable ext4 features by default

LU-419 enable ext4 features by default

Enable the flex_bg, huge_file, and dir_nlink features from ext4 by
default for ext4-based ldiskfs filesystems.  The flex_bg feature
can significantly reduce e2fsck time as well as time-to-first-write
on newly mounted OSTs.

Enable the 64bit feature for ext4 filesystems if the device size is
larger than 2^32 blocks.  This is required in order to format OSTs
larger than 16TB in size.

Reduce the number of inodes created on larger OST filesystems, since
there are far too many inodes created by default, which wastes space
and slows down e2fsck.

Skip zeroing the journal at format time.  It will be overwritten
at first use, and avoids writing 400MB of zeroes to the filesystem
needlessly.  We can't skip zering the inode table by default, but
newer mke2fs will check if the kernel handles this itself, and
request it internally.

Cleanups to remove support for 2.4 kernels and reiserfs filesystem.

Based on LU-255 commit eb012d4a10208b26c2d3e795a90f1bb07dde6d91.

Change-Id: I614003cc4d471f5fc33c379f66407e995fe856e2
Signed-off-by: Andreas Dilger <adilger@whamcloud.com>
Reviewed-on: http://review.whamcloud.com/958
Tested-by: Hudson
Reviewed-by: Yu Jian <yujian@whamcloud.com>
Reviewed-by: Johann Lombardi <johann@whamcloud.com>