Update migrations to accept migrated settings

- Unify all conditional YAML load under utils.smart_yaml_load.
- Update all setting migrations to use the smart setting test
  mixin to create the test config file.

Signed-off-by: Roberto Rosario <roberto.rosario@mayan-edms.com>

mayan/apps/smart_settings/utils.py

@@ -5,6 +5,7 @@ import os
 
 import yaml
 
+from mayan.apps.common.compat import dict_type
 from mayan.apps.common.serialization import yaml_load
 
 from .literals import (
@@ -219,6 +220,15 @@ class MediaBootstrapSetting(FilesystemBootstrapSetting):
         )
 
 
+def smart_yaml_load(value):
+    if isinstance(value, dict_type):
+        return value
+    else:
+        return yaml_load(
+            stream=value or '{}',
+        )
+
+
 # FilesystemBootstrapSetting settings
 
 SettingNamespaceSingleton.register_setting(