ConfigProviders abstract over path construction

Fixes issue where certs can't be uploaded in UI in k8s

util/config/provider/testprovider.py

@@ -1,5 +1,6 @@
 import json
 import io
+import os
 from datetime import datetime, timedelta
 
 from util.config.provider.baseprovider import BaseProvider
@@ -88,3 +89,7 @@ class TestConfigProvider(BaseProvider):
   def reset_for_test(self):
     self._config['SUPER_USERS'] = ['devtable']
     self.files = {}
+    
+  def get_volume_path(self, directory, file):
+    return os.path.join(directory, file)
+