Created the TestHarnessContext class to mantain the state of the
TestHarness and to allow the sharing of environmental variable, test case
name and a reference to the test harness.

Also changed the previously existing TestStep abstract class to be named
AbstractTestStep and then created an interface to define the TestStep
Removed the "spurious" TODO comments added by eclipse

Removed references to AbstractTestStep within harness etc (these needed to
be TestStep interface types) caused by the refactoring