LUDOC-27 mkfs.lustre: Updated descriptions for filesystem and index options.

LUDOC-27 mkfs.lustre: Updated descriptions for filesystem and index options.

Completed LUDOC-27 "documenting new mkfs.lustre features"
subtask to LUDOC-3) per instructions from Zhiqi. Edited descriptions
for the "filesystem" and "index" options to the mkfs.lustre command
in Section 36.14.

Signed-off-by: Linda Bebernes <linda.bebernes@intel.com>
Change-Id: I04e24a3f407e535d740daa1e2963168f9f30dacd
Reviewed-on: http://review.whamcloud.com/7947
Tested-by: Hudson
Reviewed-by: Richard Henwood <richard.henwood@intel.com>