[test] Ensure string secret created from files can be edited

o opensvc/tests/test mgr.py::TestCfgSecEdit
  o test can edit editable objects created from file (sec)

opensvc/core/objects/data.py

@@ -138,7 +138,11 @@ def edit(self):
         if buff is None:
             raise ex.Error("could not decode the secret key '%s'" % self.options.key)
         if isinstance(buff, bytes):
-            raise ex.Error("binary keys are not editable")
+            try:
+                self.log.debug("try decode binary key")
+                buff = buff.decode()
+            except:
+                raise ex.Error("binary keys are not editable")
         no_newline = os.sep not in try_decode(buff)
         editor = find_editor()
         fpath = self.tempfilename()

opensvc/tests/test_mgr.py

@@ -360,7 +360,7 @@ def file_editor_side_effect(_, fpath):
             assert output_file.read() == 'abcd text added'
 
     @staticmethod
-    @pytest.mark.parametrize('obj', ['demo/cfg/name'])
+    @pytest.mark.parametrize('obj', ['demo/cfg/name', 'demo/sec/name'])
     def test_can_edit_editable_objects_created_from_file(mocker, capture_stdout, tmp_file, obj):
         """
         objects created from file are bytes

opensvc/utilities/edit_file.py

@@ -2,4 +2,5 @@
 
 
 def edit_file(editor, fpath):
-    os.system(' '.join((editor, fpath)))
+    # for python 2.7 pylint disable no-member
+    os.system(' '.join((editor, fpath)))  # pylint: disable=no-member