mount: append inverting options for mount.<type> on "users"

mount: append inverting options for mount.<type> on "users"

If you call mount(8) as root, then we need to append inverting options
(if specified by fstab) for "user" and "users" to /sbin/mount.<type>
command line, because for UID=0 mount.nfs follows command line rather
than the fstab setting.

This has been originally implemented by commit
a4c0cc75ff9744299f108c259efab1bd30c8007a for the old mount(8). The
same feature is supported by libmount, unfortunately for "user" only.
We need the same also for "users" to be backwardly compatible.

Addresses: https://github.com/karelzak/util-linux/issues/368
Signed-off-by: Karel Zak <kzak@redhat.com>