tasks/nfs: make sure NFS kernel server is started
tasks/nfs: make sure NFS kernel server is started

Fixes: #9994
Signed-off-by: Yan, Zheng <5a3288024fcad83740d827e0862f4c1e6f28e7bf@redhat.com>

SUSE/teuthology,dreamhost/teuthology,SUSE/teuthology,ktdreyer/teuthology,caibo2014/teuthology,dreamhost/teuthology,SUSE/teuthology,dmick/teuthology,michaelsevilla/teuthology,michaelsevilla/teuthology,dmick/teuthology,caibo2014/teuthology,robbat2/teuthology,dmick/teuthology,ktdreyer/teuthology,robbat2/teuthology,ceph/teuthology,ceph/teuthology