LU-1526 utils: Supply default MDT index

LU-1526 utils: Supply default MDT index

To prepare for DNE indexing has become a requirement
for MDTs and with the latest lustre you can't mount
a MDT that was not formated with a index. While mount
has this requirement mkfs.lustre has a bug that allows
you to format a MDS without a index and not even warn
the user. At the same time mkfs.lustre has to handle
the case were a user will not supply a index since it
was not required in earlier lustre releases. This patch
address this problem by supplying a default index of
zero for the MDT if no index is supplied to mkfs.lustre
and warns the user they must supply a index in the
future.

Signed-off-by: James Simmons <uja.ornl@gmail.com>
Change-Id: I45932321885856d97b10630a0667e8338822b199
Reviewed-on: http://review.whamcloud.com/4293
Tested-by: Hudson
Tested-by: Maloo <whamcloud.maloo@gmail.com>
Reviewed-by: Li Wei <liwei@whamcloud.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>