(arm-16) note on hex flags not supported first release

This just adds a note that binary flags are not expected to be supported in
the first release.
(arm-16) updating open questions

This updates the open questions with our current line of thinking. This
also adds the scenario that Ethan brought up about previously managed
ACEs that have been removed and the possible surprising behavior that
might come along with that.
(arm-16) Remove :permissions => [] as valid scenario

With it being more possible that someone might have a bug in a hiera script
than to reasonably want ACLs locked down to nobody having permission,
we decided to change the support for this to what a reasonable person might
expect if they had a bug in their scripts that would cause :permissions => [].

This will cause Puppet to error and not attempt to move forward with setting
the permissions in a surprising way.