ctdb-scripts: Use nfsconf as a last resort get nfsd thread count

ctdb-scripts: Use nfsconf as a last resort get nfsd thread count

If nfsconf exists then use it as last resort to attempt to extract
[nfsd]:threads from /etc/nfs.conf.

Invocation of nfsconf requires "|| true" because this script uses "set
-e".  Add a stub that always fails to at least test this much.

RN: Use nfsconf utility for variable values in CTDB NFS scripts
BUG: https://bugzilla.samba.org/show_bug.cgi?id=14444
Signed-off-by: Martin Schwenke <martin@meltin.net>
Reviewed-by: Amitay Isaacs <amitay@gmail.com>
Autobuild-User(master): Amitay Isaacs <amitay@samba.org>
Autobuild-Date(master): Mon Jul 27 07:06:58 UTC 2020 on sn-devel-184

(cherry picked from commit 642dc6ded6426ba2fbf3ac1e5cd71aae11ca245b)