LU-16310 sec: Lustre/HSM on enc file with enc key

LU-16310 sec: Lustre/HSM on enc file with enc key

Support for Lustre/HSM on encrypted files when the encryption key is
available requires similar attention as with file migration.
The volatile file used for HSM restore must have the same encryption
context as the Lustre file being restored, so that file content
remains accessible after the layout swap at the end of the restore
procedure.

Please note that using Lustre/HSM with the encryption key creates
clear text copies of encrypted files on the HSM backend storage.

Lustre-change: https://review.whamcloud.com/49153
Lustre-commit: df7a8d92d2378e236ee83b559e7a1158f84e63f4

Signed-off-by: Sebastien Buisson <sbuisson@ddn.com>
Change-Id: I99cba202cd2c7c747bbe5c4ec7d9208c7f6baf4b
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Reviewed-by: Etienne AUJAMES <eaujames@ddn.com>
Reviewed-on: https://review.whamcloud.com/c/ex/lustre-release/+/49899
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>