LU-4293 utils: handle lfs migrate failure in lfs_migrate

LU-4293 utils: handle lfs migrate failure in lfs_migrate

If "lfs migrate" returns an error, possibly because it is refusing
to migrate an IGIF FID, fall back to using rsync to copy the file
and rename it.  Print a message in this case so the user knows it
is not a fatal error yet.

Signed-off-by: Andreas Dilger <andreas.dilger@intel.com>
Change-Id: I114006afb93d8c8d78923a874f3b914200500c1e
Reviewed-on: http://review.whamcloud.com/8616
Tested-by: Jenkins
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Faccini Bruno <bruno.faccini@intel.com>
Reviewed-by: Bob Glossman <bob.glossman@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>