Make etcd calls in callInThread

Change-Id: I3b4e28eb54440646fec050d2e2a13194c962c639
diff --git a/voltha/core/config/config_backend.py b/voltha/core/config/config_backend.py
index d906348..84b9840 100644
--- a/voltha/core/config/config_backend.py
+++ b/voltha/core/config/config_backend.py
@@ -16,6 +16,7 @@
 from common.utils.asleep import asleep
 from requests import ConnectionError
 from twisted.internet.defer import inlineCallbacks, returnValue
+from twisted.internet import reactor
 
 import etcd3
 import structlog
@@ -226,10 +227,10 @@
         return self._retry('GET', *args, **kw)
 
     def _kv_put(self, *args, **kw):
-        return self._retry('PUT', *args, **kw)
+        reactor.callInThread(self._retry, 'PUT', *args, **kw)
 
     def _kv_delete(self, *args, **kw):
-        return self._retry('DELETE', *args, **kw)
+        reactor.callInThread(self._retry, 'DELETE', *args, **kw)
 
     def _retry(self, operation, *args, **kw):