mount.nfs - NFSv4 mounts give wrong error message when server denies the mount

When nfs4 mount fail because the exported directory does
not exist, the mount command claims the local mount point
does not exist which is wrong. This patch fixes that problem
as well as  makes the v4 mount failures look like v3/v2 failures.

Signed-off-by: Steve Dickson <steved@redhat.com>
Signed-off-by: Neil Brown <neilb@suse.de>