Enables pylint W0223 lint check

Besides enabling the check, this change also makes ISO9660PyCDLib
inherit from MixInMntDirMount so it has the implementation of
mount_dir() property.
Signed-off-by: NCaio Carrara <ccarrara@redhat.com>

avocado/utils/iso9660.py

@@ -384,7 +384,7 @@ class Iso9660Mount(BaseIso9660):
         return self._mnt_dir
 
 
-class ISO9660PyCDLib(BaseIso9660):
+class ISO9660PyCDLib(MixInMntDirMount, BaseIso9660):
 
     """
     Represents a ISO9660 filesystem

selftests/checkall

@@ -169,7 +169,7 @@ results_dir_content() {
 [ "$SKIP_RESULTSDIR_CHECK" ] || RESULTS_DIR_CONTENT="$(ls $RESULTS_DIR 2> /dev/null)"
 
 LINT_CMD="inspekt lint --exclude=.git"
-PYLINT_ENABLE="--enable R0401,W0101,W0102,W0104,W0105,W0106,W0107,W0108,W0109,W0111,W0120,W0122,W0123,W0124,W0125,W0150,W0199,W0211,W0222,W0232,W0233,W0301,W0312,W0401,W0404,W0406,W0410,W0601,W0602,W0603,W0604,W0611,W0612,W0613,W0614,W0621,W0622,W0623,W0640,W0711,W1201,W1202,W1300,W1301,W1302,W1303,W1304,W1305,W1306,W1307,W1401,W1402,W1501,W1503,W1645"
+PYLINT_ENABLE="--enable R0401,W0101,W0102,W0104,W0105,W0106,W0107,W0108,W0109,W0111,W0120,W0122,W0123,W0124,W0125,W0150,W0199,W0211,W0222,W0223,W0232,W0233,W0301,W0312,W0401,W0404,W0406,W0410,W0601,W0602,W0603,W0604,W0611,W0612,W0613,W0614,W0621,W0622,W0623,W0640,W0711,W1201,W1202,W1300,W1301,W1302,W1303,W1304,W1305,W1306,W1307,W1401,W1402,W1501,W1503,W1645"
 if [ "$AVOCADO_PARALLEL_LINT" ]; then
     LINT_CMD="$LINT_CMD --parallel=$AVOCADO_PARALLEL_LINT"
 fi

selftests/unit/test_utils_iso9660.py

@@ -190,6 +190,10 @@ class PyCDLib(BaseIso9660):
             self.assertEqual(read_iso.read(path), content)
             self.assertTrue(os.path.isfile(new_iso_path))
 
+    def test_mnt_dir(self):
+        """Use the mnt_dir property"""
+        self.mnt_dir_workflow()
+
 
 if __name__ == "__main__":
     unittest.main()