Document using restraint to run autotest tests in Beaker

[ncoghlan]

The documentation of "entry_point" hints at the ability to run autotest tests in Beaker, but it would be nice to have a full walkthrough of how to take an existing autotest test and use restraint to run it in Beaker.

[ncoghlan]

beaker-devel thread regarding the lack of docs: https://lists.fedorahosted.org/pipermail/beaker-devel/2013-November/000843.html

We now also have folks trying to port existing autotest's to Beaker, and I don't know what to tell them, because I don't know how to do it.

Please, please, document this. At the moment, people are assuming it can't be done, even though autotest has had Beaker integration support since 0.15.0.