LU-12269 kernel: RHEL 8.0 server support

LU-12269 kernel: RHEL 8.0 server support

This patch makes changes to support RHEL 8.0 release
for Lustre server.

The ldiskfs patch series was added by commit
5f7bd9a806d5ba5b0e70ae1b299a9b9a87fcc0a6.

Test-Parameters: trivial \
envdefinitions=SANITY_EXCEPT="421a 817" \
clientdistro=el8 serverdistro=el8 \
testlist=sanity

Change-Id: I6380c6cb6280e49bd1b193a639f1c5cd6f4e7ef1
Signed-off-by: Jian Yu <yujian@whamcloud.com>
Reviewed-on: https://review.whamcloud.com/35665
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Wang Shilong <wshilong@ddn.com>
Reviewed-by: Yang Sheng <ys@whamcloud.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>