Add multi-node local logging to the logger

This is not yet able to forward messages, but is able to log messages
that have been forwarded.  Create a log file and test that the
timestamps are getting recorded correctly.

Change-Id: Ica891dbc560543546f6ee594438cebb03672190e
diff --git a/aos/events/shm_event_loop.cc b/aos/events/shm_event_loop.cc
index a8e227e..cde538a 100644
--- a/aos/events/shm_event_loop.cc
+++ b/aos/events/shm_event_loop.cc
@@ -155,7 +155,11 @@
 ShmEventLoop::ShmEventLoop(const Configuration *configuration)
     : EventLoop(configuration),
       name_(Filename(program_invocation_name)),
-      node_(MaybeMyNode(configuration)) {}
+      node_(MaybeMyNode(configuration)) {
+  if (configuration->has_nodes()) {
+    CHECK(node_ != nullptr) << ": Couldn't find node in config.";
+  }
+}
 
 namespace internal {