mgmt+face: move protocol-specific face creation checks into protocol factories

Also brought implementation of faces/create in line with design

refs #3731

Change-Id: I4f48079136b42c7fdbd4fdfba37116d2565f9dc1
diff --git a/daemon/face/unix-stream-factory.cpp b/daemon/face/unix-stream-factory.cpp
index 3de85b4..b85953e 100644
--- a/daemon/face/unix-stream-factory.cpp
+++ b/daemon/face/unix-stream-factory.cpp
@@ -1,6 +1,6 @@
 /* -*- Mode:C++; c-file-style:"gnu"; indent-tabs-mode:nil; -*- */
 /**
- * Copyright (c) 2014-2015,  Regents of the University of California,
+ * Copyright (c) 2014-2016,  Regents of the University of California,
  *                           Arizona Board of Regents,
  *                           Colorado State University,
  *                           University Pierre & Marie Curie, Sorbonne University,
@@ -51,7 +51,7 @@
                               const FaceCreatedCallback& onCreated,
                               const FaceCreationFailedCallback& onConnectFailed)
 {
-  BOOST_THROW_EXCEPTION(Error("UnixStreamFactory does not support 'createFace' operation"));
+  onConnectFailed(406, "Unsupported protocol");
 }
 
 std::vector<shared_ptr<const Channel>>