API change: service state nodes

[William Reade]

On Fri, 2011-12-16 at 10:12 -0200, Gustavo Niemeyer wrote:
> > As part of the machine constraints story, I propose we add a
> > "constraints" key to the service state nodes' content. This would
> (...)
> > charm: cs:oneiric/mysql-42
> > constraints: [arch=amd64, cpu=, mem=16G]
> 
> Sounds good. I'm just wondering about the choice of a string list.
> This feels like a natural fit for a map/dict.
> 

It's really just that I don't see the benefits of storing an
intermediate format -- we'll collapse all the constraints into a single
dict when we come to choosing an actual machine, but in the meantime
(*and* for the convenience of the get-constraints command that (I
presume) we'll want sooner rather than later) it seems neatest to keep
the constraints in the form in which they were originally specified. I
could surely be convinced otherwise...