provider/openstack: handle AZ IsNotImplemented

Handle goose IsNotImplemented errors relating
to availability zones. We'll propagate them up
in the case of placement, but ignore them if
doing automatic spread.

Fixes https://bugs.launchpad.net/juju-core/+bug/1330162
Merge pull request #102 from axw/lp1330162-openstack-az-notimplemented

provider/openstack: handle AZ IsNotImplemented

Handle goose IsNotImplemented errors relating to availability zones. We'll propagate them up in the case of placement, but ignore them if doing automatic spread.

Fixes https://bugs.launchpad.net/juju-core/+bug/1330162