LU-13783 osd-ldiskfs: use alloc_file_pseudo to create fake files

LU-13783 osd-ldiskfs: use alloc_file_pseudo to create fake files

With kallsyms_lookup_name() no longer exported with 5.8+ kernels
this means the work around to setup the security handling broke.
Currently osd-ldiskfs will crash due to security_alloc() never
being called. The solution is to use alloc_file_pseudo() instead
to create our fake file.

Lustre-change: https://review.whamcloud.com/43876
Lustre-commit: b0f150eba4c2ced44c3a41bcb7cfc7517f7b31f1

Change-Id: Ib417ebdda7d9829a231c568022618154c273f3e6
Signed-off-by: James Simmons <jsimmons@infradead.org>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Reviewed-on: https://review.whamcloud.com/46224
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>