LU-17212 gss: survive improper obd or imp at ctx init

LU-17212 gss: survive improper obd or imp at ctx init

GSS context init requests can happen even after a client has been
unmounted, because they are coming from userspace (request-key,
lgss_keyring).
In this case they must be ignored, and code must be robust to survive
improper, already or partially shutdown obd device or import.

Test-Parameters: kerberos=true testlist=sanity-krb5
Signed-off-by: Sebastien Buisson <sbuisson@ddn.com>
Change-Id: I541727165eadf1fcb7715e416da85d100976cf2f
Reviewed-on: https://review.whamcloud.com/c/fs/lustre-release/+/52755
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Aurelien Degremont <adegremont@nvidia.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>