the check_connection is done by querying the exports of the nfs server
in question. With nfs v4 those exports aren't listed anymore since nfs
v4 employs a pseudo-filesystem starting from root (/).
rpcinfo allows to query the existence of an nfs v4 service.
Signed-off-by: Alwin Antreich <a.antreich@proxmox.com>
89b9ac961a