LU-4569 hsm: Prevent copytool from importing existing file.

LU-4569 hsm: Prevent copytool from importing existing file.

Requesting import of an already existing FID can lead to data
corruption since both inodes in lustre would refer to the same
file in the backend.

Lustre-change: http://review.whamcloud.com/10185
Lustre-commit: 8dfee22dd5a896144fb913f5f9f0e8f5c0e4ed86

Change-Id: I92d951e3e0796c9bde8bd744f39f242e2aa233eb
Signed-off-by: Henri Doreau <henri.doreau@cea.fr>
Tested-by: Jenkins
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: jacques-Charles Lafoucriere <jacques-charles.lafoucriere@cea.fr>
Reviewed-by: Jinshan Xiong <jinshan.xiong@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>
Reviewed-on: http://review.whamcloud.com/10479
Reviewed-by: John L. Hammond <john.hammond@intel.com>