First cut ListNetworks
move filter implementation to its own package, put it behind an interface
use real NewFilter func in tests
Merge branch 'master' into listnetworks-maas
Merge branch 'master' into uniter-extract-filter
Merge branch 'master' into listnetworks-maas
Skeleton test for ListNetworks
Updated comment and logging
Add comments to test
Merge pull request #1130 from voidspace/listnetworks-maas

ListNetworks maas

An implementation of Envrion.ListNetworks for the MaaS provider. It fetches the available networks for a given instance.
add doc comments to Filter interface
Merge pull request #1128 from fwereade/uniter-extract-filter

Uniter: extract Filter

This is trivial: I just put it behind an interface, moved it to its own package, and put the tests in a _test package.
Update utils dep.
Drop Metadata.Copy().
Merge pull request #1156 from ericsnowcurrently/backups-drop-meta-Copy

Drop Copy() from backups.Metadata

http://reviews.vapour.ws/r/447/

(Review request: https://reviews.vapour.ws/r/467/)