Upgrade the 'stack' script to python3.

Also hook up the test to Android.bp.

Test: unit test
Test: Ran with a tombstone file as parameter.
Test: Ran pasting in stack to stdin.
Change-Id: I25f40569cc49b7487553611bcc25d061179bfa8d

scripts/stack

@@ -1,4 +1,4 @@
-#!/usr/bin/env python
+#!/usr/bin/env python3
 #
 # Copyright (C) 2013 The Android Open Source Project
 #
@@ -42,10 +42,10 @@ def main():
   if args.syms:
     symbol.SYMBOLS_DIR = args.syms
   if args.file == '-':
-    print "Reading native crash info from stdin"
+    print("Reading native crash info from stdin")
     f = sys.stdin
   else:
-    print "Searching for native crashes in %s" % args.file
+    print("Searching for native crashes in %s" % args.file)
     f = open(args.file, "r")
 
   lines = f.readlines()