Added boosting for certain series

Added boosts to trusty > precise > utopic > everything else.

Note I implemented this as described on the card so there is specifically no boosting to bundles, That might want to be looked at. I have made the series boost lower than the promulgated boost so all things being equal for any given charm you should see the promulgated trusty charm at the top of the list followed by the promulgated precise one etc.
? 
   c.Assert(res.Results, gc.DeepEquals, []*charm.Reference{
        exportTestCharms["mysql"],
        exportTestCharms["wordpress"],
        exportTestCharms["wordpress-simple",
        exportTestCharms["varnish"],
   }