Store UUIDs as 16 bytes of data

This makes them much more efficient to write over shared memory to solve
the boot UUID logging problem when we add them.

Change-Id: Idf361d6b096bfa52cbc98f555c90bf1f6b90d3e0
diff --git a/aos/network/message_bridge_protocol.cc b/aos/network/message_bridge_protocol.cc
index 53102c2..87114ed 100644
--- a/aos/network/message_bridge_protocol.cc
+++ b/aos/network/message_bridge_protocol.cc
@@ -13,14 +13,14 @@
 
 aos::FlatbufferDetachedBuffer<aos::message_bridge::Connect> MakeConnectMessage(
     const Configuration *config, const Node *my_node,
-    std::string_view remote_name, std::string_view boot_uuid) {
+    std::string_view remote_name, const UUID &boot_uuid) {
   CHECK(config->has_nodes()) << ": Config must have nodes to transfer.";
 
   flatbuffers::FlatBufferBuilder fbb;
   fbb.ForceDefaults(true);
 
   flatbuffers::Offset<flatbuffers::String> boot_uuid_offset =
-      fbb.CreateString(boot_uuid);
+      boot_uuid.PackString(&fbb);
 
   flatbuffers::Offset<Node> node_offset =
       RecursiveCopyFlatBuffer<Node>(my_node, &fbb);