apiserver: Extract common.InstanceIdGetter mixin

apiserver: Extract common.InstanceIdGetter mixin

Use by both the provisioner and the upcoming
firewaller server-side APIs, the InstanceId()
method is extracted to a common apiserver mixin.

https://code.launchpad.net/~dimitern/juju-core/236-apiserver-common-instanceidgetter/+merge/202352

Requires: https://code.launchpad.net/~dimitern/juju-core/235-apiserver-common-environmachineswatcher/+merge/202350

(do not edit description out of merge proposal)

[dimitern, 2014-01-20 17:51:20]

Please take a look.

[rog, 2014-01-21 14:45:54]

LGTM with one suggestion.

https://codereview.appspot.com/54650043/diff/1/state/interface.go
File state/interface.go (right):

https://codereview.appspot.com/54650043/diff/1/state/interface.go#newcode183
state/interface.go:183: type InstanceIdGetter interface {
As with my comments on a previous code review, I don't believe we need to define
all possible interfaces that might be used elsewhere here.

[dimitern, 2014-01-21 17:38:36]

https://codereview.appspot.com/54650043/diff/1/state/interface.go
File state/interface.go (right):

https://codereview.appspot.com/54650043/diff/1/state/interface.go#newcode183
state/interface.go:183: type InstanceIdGetter interface {
On 2014/01/21 14:45:54, rog wrote:
> As with my comments on a previous code review, I don't believe we need to
define
> all possible interfaces that might be used elsewhere here.

See my reply on the prereq. I think having them all here is important (due to
them defining parts of state objects interfaces).