Add preparers for sysprop

Bug: 181070625
Test: m nothing
Change-Id: I3c9c36e7270b68ff7d354acb239b47441335a931
diff --git a/sysprop/Android.bp b/sysprop/Android.bp
index 540a8da..1d5eb31 100644
--- a/sysprop/Android.bp
+++ b/sysprop/Android.bp
@@ -14,6 +14,7 @@
     ],
     srcs: [
         "sysprop_library.go",
+        "testing.go",
     ],
     testSrcs: [
         "sysprop_test.go",