Renames admin _config var for clarity

There's already a `.config` attribute in the sdconfig flow, so let's
rename `._config` -> `._config_in_progress` to make the intended use
case explicit to future maintainers. The contents of the
_config_in_progress dict are consulted during validation steps as part
of `sdconfig`.

admin/securedrop_admin/__init__.py

@@ -169,7 +169,7 @@ def validate(self, document):
             # Raise error if admin tries to disable v3 when v2
             # is already disabled.
             if text == 'no' and \
-                    not self.caller._config.get("v2_onion_services"):
+                    not self.caller._config_in_progress.get("v2_onion_services"):  # noqa: E501
                 raise ValidationError(message="Since you disabled v2 onion services, you must enable v3 onion services.")  # noqa: E501
             if text == 'yes' or text == 'no':
                 return True
@@ -276,8 +276,9 @@ def validate(self, document):
     def __init__(self, args):
         self.args = args
         self.config = {}
-        # This is to hold runtime configuration before save
-        self._config = {}
+        # Hold runtime configuration before save, to support
+        # referencing other responses during validation
+        self._config_in_progress = {}
         translations = SiteConfig.Locales(
             self.args.app_path).get_translations()
         translations = " ".join(translations)
@@ -464,23 +465,23 @@ def check_for_v3_onion(self):
         """
         Check if v3 onion services should be enabled by default or not.
         """
-        v2_value = self._config.get("v2_onion_services", False)
+        v2_value = self._config_in_progress.get("v2_onion_services", False)
         # We need to see the value in the configuration file
         # for v3_onion_services
         v3_value = self.config.get("v3_onion_services", True)
         return v3_value or not v2_value
 
     def user_prompt_config(self):
-        self._config = {}
+        self._config_in_progress = {}
         for desc in self.desc:
             (var, default, type, prompt, validator, transform,
                 condition) = desc
-            if not condition(self._config):
-                self._config[var] = ''
+            if not condition(self._config_in_progress):
+                self._config_in_progress[var] = ''
                 continue
-            self._config[var] = self.user_prompt_config_one(desc,
+            self._config_in_progress[var] = self.user_prompt_config_one(desc,
                                                             self.config.get(var))  # noqa: E501
-        return self._config
+        return self._config_in_progress
 
     def user_prompt_config_one(self, desc, from_config):
         (var, default, type, prompt, validator, transform, condition) = desc

admin/tests/test_securedrop-admin.py

@@ -799,7 +799,7 @@ def verify_prompt_boolean_for_v3(
         # Now we will set v2_onion_services as True so that we
         # can set v3_onion_service as False. This is the case
         # when an admin particularly marked v3 as False.
-        site_config._config = {"v2_onion_services": True}
+        site_config._config_in_progress = {"v2_onion_services": True}
         site_config.config = {"v3_onion_services": False}
 
         # The next two tests should use the default from the above line,