Add NodeEventLoopFactory

This lets us create event loops on separate nodes which can't
communicate with each other.  Next step is to add a message proxy
between them, then teach the logger to replay onto multiple nodes.

Change-Id: I06b2836365aea13d696535c52a78ca0c862a7b1e
diff --git a/aos/configuration.cc b/aos/configuration.cc
index a40c47c..095add5 100644
--- a/aos/configuration.cc
+++ b/aos/configuration.cc
@@ -591,6 +591,7 @@
   }
   return nullptr;
 }
+
 const Node *GetMyNode(const Configuration *config) {
   const std::string hostname = (FLAGS_override_hostname.size() > 0)
                                    ? FLAGS_override_hostname
@@ -616,6 +617,8 @@
   return nullptr;
 }
 
+bool MultiNode(const Configuration *config) { return config->has_nodes(); }
+
 bool ChannelIsSendableOnNode(const Channel *channel, const Node *node) {
   if (node == nullptr) {
     return true;