Loader: use the DiscoverMode enum

Avocado 69.0 (LTS) already contains loader.DiscoverMode, so it's safe
to just use it directly here.
Signed-off-by: NCleber Rosa <crosa@redhat.com>

avocado_vt/loader.py

@@ -34,14 +34,6 @@ from .options import VirtTestOptionsProcess
 from .test import VirtTest
 
 
-if hasattr(loader, "DiscoverMode"):
-    LOADER_DEFAULT = loader.DiscoverMode.DEFAULT
-    LOADER_ALL = loader.DiscoverMode.ALL
-else:
-    LOADER_DEFAULT = loader.DEFAULT
-    LOADER_ALL = loader.ALL
-
-
 LOG = logging.getLogger("avocado.app")
 
 
@@ -205,12 +197,12 @@ class VirtTestLoader(loader.TestLoader):
 
     @staticmethod
     def _report_bad_discovery(name, reason, which_tests):
-        if which_tests is LOADER_ALL:
+        if which_tests is loader.DiscoverMode.ALL:
             return [(NotAvocadoVTTest, {"name": "%s: %s" % (name, reason)})]
         else:
             return []
 
-    def discover(self, url, which_tests=LOADER_DEFAULT):
+    def discover(self, url, which_tests=loader.DiscoverMode.DEFAULT):
         try:
             cartesian_parser = self._get_parser()
         except Exception as details:
@@ -225,7 +217,8 @@ class VirtTestLoader(loader.TestLoader):
             # the other test plugins to handle the URL.
             except cartesian_config.ParserError as details:
                 return self._report_bad_discovery(url, details, which_tests)
-        elif which_tests is LOADER_DEFAULT and not get_opt(self.args, 'vt_config'):
+        elif (which_tests is loader.DiscoverMode.DEFAULT and
+              not get_opt(self.args, 'vt_config')):
             # By default don't run anything unless vt_config provided
             return []
         # Create test_suite
@@ -249,7 +242,7 @@ class VirtTestLoader(loader.TestLoader):
             test_parameters = {'name': test_name,
                                'vt_params': params}
             test_suite.append((VirtTest, test_parameters))
-        if which_tests is LOADER_ALL and not test_suite:
+        if which_tests is loader.DiscoverMode.ALL and not test_suite:
             return self._report_bad_discovery(url, "No matching tests",
                                               which_tests)
         return test_suite