LU-80 tests: large xattr support

LU-80 tests: large xattr support

This patch adds and updates some test cases to verify the
large xattr feature. To enable this feature, the "-O large_xattr"
option needs to be set on the filesystem either with --mkfsoptions
at format time or via tune2fs.

Signed-off-by: Yu Jian <yujian@whamcloud.com>
Change-Id: Ie62e6e2194fdaa7239ec4e1451a4e696888dca8c
Reviewed-on: http://review.whamcloud.com/1880
Tested-by: Hudson
Tested-by: Maloo <whamcloud.maloo@gmail.com>
Reviewed-by: James Simmons <uja.ornl@gmail.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>