nbd-proxy: add configuration facility

Add a little configuration facility. We'll later add a method to
integrate this with UI-side configuration, so it's implmented as json.

We add a (temporarily required) argument to specify which configuration
to use.

Signed-off-by: Jeremy Kerr <jk@ozlabs.org>
diff --git a/Makefile.am b/Makefile.am
index 6ee7fe1..8e0d140 100644
--- a/Makefile.am
+++ b/Makefile.am
@@ -1,3 +1,9 @@
 sbin_PROGRAMS = nbd-proxy
 
-nbd_proxy_CPPFLAGS = -DRUNSTATEDIR=\"$(runstatedir)\"
+nbd_proxy_CPPFLAGS = \
+	$(JSON_CFLAGS) \
+	-DRUNSTATEDIR=\"$(runstatedir)\" \
+	-DSYSCONFDIR=\"$(sysconfdir)\"
+
+nbd_proxy_LDADD = \
+	$(JSON_LIBS)