LU-13219 tests: add nfs-server service in setup-nfs.sh

LU-13219 tests: add nfs-server service in setup-nfs.sh

For RHEL 8.1, the NFS server service is nfs-server
instead of nfs.

Test-Parameters: trivial \
clientdistro=el8.1 serverdistro=el8.1 \
testlist=parallel-scale-nfsv3,parallel-scale-nfsv4

Change-Id: I5a97c8fe419187412dfc02047ed66141f567d7fb
Signed-off-by: Jian Yu <yujian@whamcloud.com>
Reviewed-on: https://review.whamcloud.com/37663
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: James Nunez <jnunez@whamcloud.com>
Reviewed-by: Wei Liu <sarah@whamcloud.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>