move dbus helper interface into its own file

This is step 1 to improving the interface to be more generic and drop
requirements on dbus.

Signed-off-by: Patrick Venture <venture@google.com>
Change-Id: I7835ea8242bfb7189cabc1a4084e5f84143d40f6
diff --git a/Makefile.am b/Makefile.am
index edbebfa..728fe8a 100644
--- a/Makefile.am
+++ b/Makefile.am
@@ -81,7 +81,8 @@
 libswampd_la_SOURCES = \
 	notimpl/readonly.cpp \
 	notimpl/writeonly.cpp \
-	dbus/util.cpp \
+	dbus/dbusutil.cpp \
+	dbus/dbushelper.cpp \
 	dbus/dbuspassiveredundancy.cpp \
 	dbus/dbuspassive.cpp \
 	dbus/dbusactiveread.cpp \