Move modules.bzl from root down into the bazel tools directory

Change-Id: I6ccaa07e88914537d07dea63b36ee243b152b41a
diff --git a/BUILD b/BUILD
index 69e31ee..dd60f38 100644
--- a/BUILD
+++ b/BUILD
@@ -1,5 +1,5 @@
 load("//tools/build/bazel:variables.bzl", "ONOS_VERSION")
-load(":modules.bzl", "APPS", "CORE", "FEATURES")
+load("//tools/build/bazel:modules.bzl", "APPS", "CORE", "FEATURES")
 
 filegroup(
     name = "onos",