LU-4293 mdd: Allow layout swap for IGIF FIDs

LU-4293 mdd: Allow layout swap for IGIF FIDs

Patch to also allow layout swap for pre-2.x migrated
files (ie, IGIF FID with linkEA).

Root user special case has also been added to lfs/migrate
command to map owner/group of original file to
volatile, in order to comply with other layout_swap rules.

Signed-off-by: Bruno Faccini <bruno.faccini@intel.com>
Change-Id: Ia7e7cb2e6e36ba67a57474b8a806a53257a3e014
Reviewed-on: http://review.whamcloud.com/8737
Reviewed-by: Andreas Dilger <andreas.dilger@intel.com>
Tested-by: Jenkins
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: John L. Hammond <john.hammond@intel.com>