Use comments to skip tests instead of a tag

Lettuce behaves strangely with "exclude" tags.  If you have a scenario marked with two tags:

    @skip @tag_1
    Scenario: ...

And you run lettuce with `--tag -skip -tag tag_1` (EXCLUDE `skip`, INCLUDE `tag_1`), then the scenario will get run.  Looking at the code, lettuce seems to handle this inconsistently: if a scenario has just ONE tag, then it will be run only if it satisfies ALL the specified tags.

I'm going to submit a PR later to the lettuce project, but until then, the quick fix is to comment out the scenarios instead of relying on `skip` tags.  This will allow me to correctly shard the tests in the Jenkins cluster.

@jzoldak