test mcollective::user::setting

Having written this I wonder if it should instead delegate to
mcollective::setting with some kind of scope => 'mcollective::user $username',

It's extra indirection but it might make it more obvious.  Also it reduces the
places we expose datacat, for if we need to rip that out.
recast all ::setting classes in terms of mcollective::setting

It's a reduced surface area for replacing datacat, plus we can
double-check values from the specs now.