Code review comment for lp:~fwereade/juju-core/bootstrap-constraints-2

LGTM

https://codereview.appspot.com/7610048/diff/1/environs/bootstrap_test.go
File environs/bootstrap_test.go (right):

https://codereview.appspot.com/7610048/diff/1/environs/bootstrap_test.go#newcode39
environs/bootstrap_test.go:39: err := environs.Bootstrap(env,
state.Constraints{}, false, nil)
+1, as it also means the struct doesn't get copied when it doesn't need
to. Though I suppose we want to avoid the side-effect of passing in
constraints and then changing the in-memory struct later?
But that could just be the final e.constraints = *cons (so it does do an
explicit copy at that point).

https://codereview.appspot.com/7610048/