Allow to build Android.bp in tradefed project

We want to start using some Soong Android.bp in tradefed so
enabling our project to be seen too.

Test: build a Android.bp target in tradefed
Bug: 66908811
Change-Id: Ia4543fc27d124442912e3a05d7bd3fd2f9850a1f
diff --git a/root.bp b/root.bp
index f27d28b..6788fa7 100644
--- a/root.bp
+++ b/root.bp
@@ -37,6 +37,7 @@
     "test/vts",
     "test/vts-testcase/*",
     "tools/*",
+    "tools/tradefederation/*",
     "toolchain/*",
     "vendor/*/*",
 ]