Code review comment for lp:~axwalk/juju-core/instances-arch-preference

Reviewers: mp+219839_code.launchpad.net,

Message:
Please take a look.

Description:
Fix arch preference algorithm

Change the instance architecture preference
selection to widest word-size, then first
arch name by alphabetical order. For tie-
breakers, choose the instance type based on
provider-specific ordering.

In the future we may want to extend the
ordering to include cost. For now, we rely
on the providers ordering instance types by
their own preference (no change here).

https://code.launchpad.net/~axwalk/juju-core/instances-arch-preference/+merge/219839

(do not edit description out of merge proposal)

Please review this at https://codereview.appspot.com/94530045/

Affected files (+76, -58 lines):
   A [revision details]
   M environs/instances/image.go
   M environs/instances/image_test.go
   M juju/arch/arch.go
   M juju/arch/arch_test.go