LU-12395 build: build mpitests for el8

LU-12395 build: build mpitests for el8

RHEL8 has rpm-mpi-hooks which requires binaries
to be in specific mpi bin to generate the correct
requires

See https://fedoraproject.org//wiki/Changes/RpmMPIReqProv
and https://fedoraproject.org/wiki/Packaging:MPI

Test-Parameters: trivial clientdistro=el8 serverdistro=el7.6 testgroup=regression-mpi

Lustre-change: https://review.whamcloud.com/35374
Lustre-commit: 3c7aca74729edb5339d2b84259ba042bf83c214a

Change-Id: Id9fa50e15b48b9da846083b9e9cd894ad1eac967
Signed-off-by: Minh Diep <mdiep@whamcloud.com>
Reviewed-by: Jian Yu <yujian@whamcloud.com>
Reviewed-by: Yang Sheng <ys@whamcloud.com>
Reviewed-by: Li Dongyang <dongyangli@ddn.com>
Signed-off-by: Minh Diep <mdiep@whamcloud.com>
Reviewed-on: https://review.whamcloud.com/35473
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>