Add TravisCI config

In preperation for enabling TravisCI to run lint and unit tests against our
pull requests. This:

- Uses the Ruby defaults such as `bundle install` and `bundle exec rake`.
- Only tests 1.9.3 at the moment, which I think is what we're targetting?
  But we might want to extend it to 2.x in the future.
- Doesn't test against master because that is handled by our in-house CI
  system which also runs integration tests.
- Disables email notifications because we already get a lot of email and the
  PR status hook on GitHub should be good enough.
Simplify EdgeGatewayInterface defenses

EdgeGatewayInterface is an internal-use class, we don't need
to be excessive with the input checking.

Simplified the input checking to ensure that we don't unnecessarily
create NilClass exceptions.

Tests adjusted tests accordingly.
Merge pull request #39 from alphagov/70499778-add_travis_config

[#70499778] Add TravisCI config
Merge pull request #42 from alphagov/improve_bad_input_handling_clarity

[#70437918] Simplify EdgeGatewayInterface defenses
Move from deprecated get_network call

... to get_network_complete.

The get_network request rewrites the output from the vCloud API, and loses information
in the process. It has been deprecated in Fog since 1.21.

The discussion surrounding this deprecation is in https://github.com/fog/fog/pull/2683

As a result, this commit alters the output of OrgVdcNetwork#vcloud_attributes,
making it more closely reflect the output from the vCloud API, rather than the
re-written output of get_network.

At the moment, the only place known to be using vcloud_attributes are the
integration tests for http://github.com/alphagov/vcloud-net_launcher
Update CHANGELOG detailing OrgVdcNetwork change
Bump version to 0.3.0 (breaking changes)
Merge pull request #45 from alphagov/70443650_get_network_deprecation

[#70443650] Replace deprecated get_network call
Merge branch 'master' into 70437918_erb_vars_handling
Anchor post processor output matcher

So that we reduce the potential for false positives