LU-12634 gss: uid_keyring and session_keyring moved

LU-12634 gss: uid_keyring and session_keyring moved

Linux 5.3 removed uid_keyring and session_keyring from user_struct
Prefer the lookup_user_key() API when it is available (~5.0)
Prefer get_request_key_auth() when it is available (~5.0)

kernel-commit: 0f44e4d976f96c6439da0d6717238efa4b91196e
kernel-commit: 822ad64d7e46a8e2c8b8a796738d7b657cbb146d

Remove LC_HAVE_CRED_TGCRED which is no longer used.

Lustre-commit: 97301a491d46cf2cf829185b52b8690287ab7ed6
Lustre-change: https://review.whamcloud.com/35743

Test-Parameters: trivial
Cray-bug-id: LUS-7689
Signed-off-by: Shaun Tancheff <stancheff@cray.com>
Change-Id: I6d551cd8a9e317b717a43cba9be57f184a281c0a
Reviewed-on: https://review.whamcloud.com/40354
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Sebastien Buisson <sbuisson@ddn.com>
Reviewed-by: Petros Koutoupis <petros.koutoupis@hpe.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>