Minimal working implementation on network-get hook tool on MAAS

[dimitern]

Tested with a couple of simple charms based on the ubuntu charm, but with
a few relations, which can be bound to spaces and later the addresses we
get from network-get within each relation are logged.

Key changes:

• network.Address, params.Address, and state.address now have SpaceName added.
• instance.Addresses() in MAAS parse the interface_set map and return the space
  each IP is bound to (according to the links of each interface).
• state/API endpoints now are selected first from the default space, if possible,
  which solves the problems with non-deterministic address picking and sorting.
  As a fallback, the old approach with scopes + sorting is used.
• StartInstance() now includes EndpointBindings map, populated by the provisioner
  with all bindings from all services which have units assigned to the machine we're
  about to provision. This also takes full advantage of the "interfaces=" argument
  in MAAS (acquireNode) for bindings.

Next step should be to do the multi-NIC containers in a simplified way.

(Review request: http://reviews.vapour.ws/r/3448/)

[dimitern]

$$merge$$

[jujubot]

Status: merge request accepted. Url: http://juju-ci.vapour.ws:8080/job/github-merge-juju