mgmt+tools: rework FacePersistency handling in faces/create and faces/update

1. enable changing persistency in faces/update command
2. reject faces/create request if the face already exists
3. nfdc changes to support the above

Change-Id: I659906da846608a42a768f08fb110ceee1a947a7
refs: #3232
diff --git a/tests/daemon/mgmt/face-manager-command-fixture.hpp b/tests/daemon/mgmt/face-manager-command-fixture.hpp
index 0bde982..bf376f5 100644
--- a/tests/daemon/mgmt/face-manager-command-fixture.hpp
+++ b/tests/daemon/mgmt/face-manager-command-fixture.hpp
@@ -45,7 +45,14 @@
   ~FaceManagerCommandNode();
 
 public:
-  ndn::util::DummyClientFace face; ///< internal client face used by management
+  const Face*
+  findFaceByUri(const std::string& uri) const;
+
+  FaceId
+  findFaceIdByUri(const std::string& uri) const;
+
+public:
+  ndn::util::DummyClientFace face;
   ndn::mgmt::Dispatcher dispatcher;
   shared_ptr<CommandAuthenticator> authenticator;