Add topics attribute and validate topics

[nanduni-nin]

• Add topics attribute to the manifest specification.
• Add topics as an attribute to the manifest class.
• Allow topic attribute as an optional parameter and report missing topics as a warning.
• Report when topics are not in an array.
• Create testlib.manifest for unit testing the topics.
• Create a test example.

[cornelius]

The extension of the Manifest class and the schemas looks right.

The verification is not complete, though. It needs to be hooked up to the methods which are called when the verify command is called from the command line.

The output should not happen in the verificiation method, but with the existing methods printing also the errors. As we want to introduce a warning here, we need to extend this code. Have a look at the Verifier::Results class.

For testing it would be better to write isolated tests, which don't require modification of test data, which is used by other tests (see e.g. the manifest-all or the count of the manifests). The current admittedly is not great there, as many tests depend on shared test data. We should do this in a cleaner way for new tests.

Maybe it would be helpful to start from an integration test, which specifies what we want to achieve in the end. A test could look like this (in cli_verify_spec.rb):

    it "verifies manifests with topics warning" do
      dir = given_directory do
        given_directory_from_data("awesomelib", from: "manifests/awesomelib")
        given_directory_from_data("missing-topics")
      end

      result = run_command(args: ["verify", "--offline", "--manifest_dir=#{dir}"])
      expected_output = <<EOT
Verify manifest awesomelib.2013-09-08.manifest...ok
Verify manifest missing-topics.manifest...ok
  Warning: missing `topics` attribute

2 manifests checked. 1 ok, 0 with error, 1 with warning.
EOT
      expect(result).to exit_with_success(expected_output)
    end

[cornelius]

I added a test for the Verifier::Result class. This should help with implementing the warning functionality.