avocado.core.test: Use self.log rather than stacktrace.log_message

The use of stacktrace.log_message is not really necessary as the test
already has `self.log` which is the actual log we want to write to.
Signed-off-by: NLukáš Doktor <ldoktor@redhat.com>

avocado/core/test.py

@@ -453,12 +453,10 @@ class Test(unittest.TestCase):
             if not isinstance(details, Exception):  # Avoid passing nasty exc
                 details = exceptions.TestError("%r: %s" % (details, details))
             test_exception = details
-            stacktrace.log_message('Local variables:', logger='avocado.test')
+            self.log.debug("Local variables:")
             local_vars = inspect.trace()[1][0].f_locals
             for key, value in local_vars.iteritems():
-                stacktrace.log_message(' -> %s %s: %s'
-                                       % (key, type(value), value),
-                                       logger='avocado.test')
+                self.log.debug(' -> %s %s: %s', key, type(value), value)
         finally:
             try:
                 self.tearDown()