cylc test-battery: Expand battery 1

First of a number of forthcoming expansions to the test battery.

This makes the following additions:
 * check the documentation is buildable
 * check the example suites validate
 * check the jobfile has been constructed in the right order
 * check command scripting, pre and post scripting and environment variables have been created correctly in the generated jobfile in the case of multi-inheritance

I'll be looking into further expanding the jobfile tests in a future pull request to things like remote settings, event hooks and making sure Jinja2 content has been expanded properly but the tests here should at least cover the basics.

@hjoliver - please review.