Azure provider: delete Virtual Network

Azure provider: delete Virtual Network

This branch adds the deletion of the environment's Virtual Network and Affinity Group when the environment is destroyed.  I could have divided the test TestDestroyDeletesVirtualNetworkAndAffinityGroup into two separate tests but since the initialization of the test is pretty long and, conceptually, the Virtual Network and the Affinity Group are linked together, I decided to go with one test.

https://code.launchpad.net/~rvb/juju-core/delete-vnet-ag/+merge/175787

(do not edit description out of merge proposal)

[rvb, 2013-07-19 14:24:29]

Please take a look.

[fwereade, 2013-07-19 16:06:15]

one question, but looking good

https://codereview.appspot.com/11578043/diff/1/environs/azure/environ.go
File environs/azure/environ.go (right):

https://codereview.appspot.com/11578043/diff/1/environs/azure/environ.go#newc...
environs/azure/environ.go:679: insts, err := env.AllInstances()
Hey, does this return ErrNoInstances if there aren't any? If so, we'll still
need to delete the virtual network and the affinity group (sometimes
destroy-environment will fail halfway through... eg just after successfully
destroying all instances).

Could use a test for that case either way.

[rvb, 2013-07-19 17:23:12]

https://codereview.appspot.com/11578043/diff/1/environs/azure/environ.go
File environs/azure/environ.go (right):

https://codereview.appspot.com/11578043/diff/1/environs/azure/environ.go#newc...
environs/azure/environ.go:679: insts, err := env.AllInstances()
On 2013/07/19 16:06:15, fwereade wrote:
> Hey, does this return ErrNoInstances if there aren't any? If so, we'll still
> need to delete the virtual network and the affinity group (sometimes
> destroy-environment will fail halfway through... eg just after successfully
> destroying all instances).
> 
> Could use a test for that case either way. 

AllInstances() cannot return ErrNoInstances.  Only Instances() does that.  This
seems to follow the doc in environs/interface.go, did we interpret that doc too
strictly?

[rog, 2013-07-23 10:06:30]

LGTM

https://codereview.appspot.com/11578043/diff/1/environs/azure/environ.go
File environs/azure/environ.go (right):

https://codereview.appspot.com/11578043/diff/1/environs/azure/environ.go#newc...
environs/azure/environ.go:679: insts, err := env.AllInstances()
On 2013/07/19 17:23:12, rvb wrote:
> On 2013/07/19 16:06:15, fwereade wrote:
> > Hey, does this return ErrNoInstances if there aren't any? If so, we'll still
> > need to delete the virtual network and the affinity group (sometimes
> > destroy-environment will fail halfway through... eg just after successfully
> > destroying all instances).
> > 
> > Could use a test for that case either way. 
> 
> AllInstances() cannot return ErrNoInstances.  Only Instances() does that. 
This
> seems to follow the doc in environs/interface.go, did we interpret that doc
too
> strictly?

That seems just right. It's not an error for AllInstances to return no
instances.