LU-3867 utils: llapi_create_volatile_idx uses 0 instead idx

LU-3867 utils: llapi_create_volatile_idx uses 0 instead idx

If llapi_create_volatile_idx() is passed an MDT index other than
-1, it always uses 0 as the MDT index rather than the one provided.

This patch removes the use of LUSTRE_VOLATILE_IDX and uses
LUSTRE_VOLATILE_HDR with the MDT index instead, uses the provided
MDT index in the volatile file name and uses base 16 when reading
the MDT index from the file name using strtoul.

Signed-off-by: James Nunez <james.a.nunez@intel.com>
Signed-off-by: Bobbie Lind <bobbie.j.lind@intel.com>
Change-Id: I27e2beb8524683aba07c48297614dd02d7957af4
Reviewed-on: http://review.whamcloud.com/7613
Tested-by: Jenkins
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: John L. Hammond <john.hammond@intel.com>
Reviewed-by: Andreas Dilger <andreas.dilger@intel.com>