LU-16816 obdclass: make import_event more robust

LU-16816 obdclass: make import_event more robust

Make mdc_import_event and osc_import_event more robust, by not
assuming input variables can be dereferenced.

Test-Parameters: trivial
Signed-off-by: Sebastien Buisson <sbuisson@ddn.com>
Change-Id: I31a6477d58b7bb9a557ea561f7b0fa3fbcae5762
Reviewed-on: https://review.whamcloud.com/c/fs/lustre-release/+/50915
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Reviewed-by: Patrick Farrell <pfarrell@whamcloud.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>