Split TestHelpers, one for JobHandler and one for EventHandler

[jcredding]

This splits the test helpers into two mixins, one for JobHandler
and one for EventHandler. This is so each can provide a different
test_runner method and in general, different test helpers as
needed.

This renames the TestRunner to JobTestRunner and adds an
EventTestRunner that inherits from it. The EventTestRunner
checks that its passed an EventHandler and also sets up passing
an event job. EventHandler, unlike JobHandler, requires its
runner to have an event job. To handle this, the EventTestRunner
will build an event job and super it to the TestRunner. It also
handles params so it can easily be passed event params directly.

This also fixes a minor issue with how the Runner set its
attributes and built its handler. Since event handlers require
their runner to have an event job when they are built, the base
Runner needs to set its attributes before it builds an instance
of the handler.

@kellyredding - Ready for review.

[kellyredding]

@jcredding we discussed you could just rename test runner as "job test runner and have the event test runner subclass. That job handler check shouldn't fail on event handlers since they bring job handler in.

[kellyredding]

@jcredding made a couple of comments. I'd like to take a second look and see how you choose to address them.

[jcredding]

@kellyredding - I've updated this. I renamed the TestRunner to JobTestRunner and changed the Factory usage to just hard-coded strings.

[kellyredding]

@jcredding very cool - I like it. 👎