Make testname and creation of TestInsertionMojo configurable.

* Instead of disabling test-injection by reconfiguring the plugin
  provide a property which is easily overridden.
* By renaming the injected test to InjectIT the test is not run
  during phase test but e.g. via the failsafe-plugin during phase
  integration-test.
Merge pull request #6 from mfriedenhagen/configurable

Make testname and creation of TestInsertionMojo configurable.