Make boot_uuid change in event loops when it changes

We were seeing any event loops created before the UUID changes staying
the same.  This defeats the purpose.  This is especially true for the
simulated network bridge which uses an event loop to get the boot UUID,
and wants to observe when it changes.

The boot UUID shouldn't change in any other conditions, so this won't
have an effect on anything else.

Change-Id: Idfa8f36e8d0e4ba964d09bf2170cbbffb17b8276
diff --git a/aos/events/shm_event_loop.cc b/aos/events/shm_event_loop.cc
index 2a0d332..39ce8db 100644
--- a/aos/events/shm_event_loop.cc
+++ b/aos/events/shm_event_loop.cc
@@ -222,7 +222,8 @@
 }  // namespace
 
 ShmEventLoop::ShmEventLoop(const Configuration *configuration)
-    : EventLoop(configuration, UUID::BootUUID()),
+    : EventLoop(configuration),
+      boot_uuid_(UUID::BootUUID()),
       shm_base_(FLAGS_shm_base),
       name_(FLAGS_application_name),
       node_(MaybeMyNode(configuration)) {