Add ability to plug specific test report parsing capabilities into Builder

Currently, the AbstractBuilder class is hard coded to use the AntJunitTestReportCollector for it's parsing of test results, which means that test results either need to be in the JUnit report format, or a test report-specific Builder plugin must be developed to parse non-JUnit report formats.

It would be nice if the test report format could be specified on the Builder configuration, so that support for other testing formats could be added without the extra overhead of creating a entire new plugin. Perhaps the test report parsing logic could be factored out into a plugin type of it's own?