Code review comment for lp://staging/~wallyworld/juju-core/move-assignment-policy

Reviewers: mp+165983_code.launchpad.net,

Message:
Please take a look.

Description:
Move assignment policy to global env config

Previoysly, each provider defined it's own AssignmentPolicy,
which was hard coded to AssignNew. Now, it's been made an
env setting with default AssignNew. With containers, it will be
possible to add a unit to an existing machine (if not dirty) so
this work is a step in that direction.

https://code.launchpad.net/~wallyworld/juju-core/move-assignment-policy/+merge/165983

Requires:
https://code.launchpad.net/~wallyworld/juju-core/add-machine-dirty-flag/+merge/165954

(do not edit description out of merge proposal)

Please review this at https://codereview.appspot.com/9824043/

Affected files:
   A [revision details]
   M environs/config/config.go
   M environs/config/config_test.go
   M environs/dummy/environs.go
   M environs/ec2/ec2.go
   M environs/ec2/local_test.go
   M environs/interface.go
   M environs/maas/environ.go
   M environs/maas/environ_test.go
   M environs/openstack/local_test.go
   M environs/openstack/provider.go
   M juju/conn.go
   M state/assign_test.go
   M state/bench_test.go
   M state/state.go
   M state/unit.go