Optimize integration testing

- Add injection package plug-in
- Add libstellar_dynamic.so to facilitate unit testing of upper-level plug-ins

test/packet_inject/version.map

@@ -0,0 +1,7 @@
+LIBPACKET_INJECT_PLUGIN {
+global:
+	packet_inject_plugin_init;
+	packet_inject_plugin_exit;
+
+local: *;
+};