Use gomaasapi MAAS 2 controller

[voidspace]

Update the MAAS provider to start using the new 2.0 API Controller from gomaasapi.

The provider will now use the Controller when working with MAAS 2.0.
Test infrastructure support for MAAS 2 tests.
Update dependencies.tsv to use the new gomaasapi.
A new method to tell if we're using MAAS 2, plus using it in a couple of places to get us slightly further on in bootstrap.

(Review request: http://reviews.vapour.ws/r/4380/)

[voidspace]

$$merge$$

[jujubot]

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

[jujubot]

Build failed: Tests failed
build url: http://juju-ci.vapour.ws:8080/job/github-merge-juju/7142

[voidspace]

$$merge$$

[jujubot]

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