avocado/core/runner.py: result is actually a TestResultProxy

Fix the docstring that doesn't reflect that the result parameter
should actually be a TestResultProxy.
Signed-off-by: NCleber Rosa <crosa@redhat.com>

avocado/core/runner.py

@@ -166,7 +166,7 @@ class TestRunner(object):
         Creates an instance of TestRunner class.
 
         :param job: an instance of :class:`avocado.core.job.Job`.
-        :param test_result: an instance of :class:`avocado.core.result.TestResult`.
+        :param test_result: an instance of :class:`avocado.core.result.TestResultProxy`.
         """
         self.job = job
         self.result = test_result