LU-2922 ldiskfs: depend on e2fsprogs-1.42.6.wc2

This patch updates lustre-ldiskfs.spec.in to depend on
a newer e2fsprogs-1.42.6.wc2 release instead of the
old 1.41.12.2.ora1 version.

Signed-off-by: Jian Yu <jian.yu@intel.com>
Change-Id: I58828fa5427e5f50cfb3b285f980e946e7eb62e7
Reviewed-on: http://review.whamcloud.com/5623
Reviewed-by: Andreas Dilger <andreas.dilger@intel.com>
Reviewed-by: Brian J. Murrell <brian.murrell@intel.com>
Tested-by: Hudson
Tested-by: Maloo <whamcloud.maloo@gmail.com>