make specification of fabric interfaces configurable

Change-Id: Id6db46e3bb0c13d1c2916255c5bd6419bc906e4b
(cherry picked from commit b247b1d3efa81b3d1fa5b30be537d5d50c5c18c8)
diff --git a/build.gradle b/build.gradle
index 0f50779..c54afc0 100644
--- a/build.gradle
+++ b/build.gradle
@@ -296,6 +296,7 @@
             .p(config.seedServer.fabric_ip, "fabric_ip")
             .p(config.seedServer.fabric_network, "fabric_network")
             .p(config.seedServer.fabric_iface, "fabric_iface")
+            .p(config.seedServer.fabric_iface_spec, "fabric_iface_spec")
             .p(config.seedServer.domain, "domain")
 	    .p(config.seedServer.virtualbox_support, "virtualbox_support")
             .p(config.seedServer.power_helper_user, "power_helper_user")
@@ -354,6 +355,7 @@
 	    .p(config.seedServer.fabric_ip, "fabric_ip")
 	    .p(config.seedServer.fabric_network, "fabric_network")
 	    .p(config.seedServer.fabric_iface, "fabric_iface")
+            .p(config.seedServer.fabric_iface_spec, "fabric_iface_spec")
             .p(config.seedServer.domain, "domain")
             .p(config.seedServer.virtualbox_support, "virtualbox_support")
 	    .p(config.seedServer.power_helper_user, "power_helper_user")