Convert findleaves.py to python 3

Kati special-cases findleaves.py to an internal
C++ implementation, so I don't think this python
script is even used. Update it anyways, and
test by manually running findleaves.py.

Bug: 203436762
Test: ./build/make/tools/findleaves.py --mindepth=2 --dir=build/make/target Android.mk
Change-Id: If27cc37d8f673388c0e31b9491e792b98ca59da4

tools/findleaves.py

@@ -1,4 +1,4 @@
-#!/usr/bin/env python
+#!/usr/bin/env python3
 #
 # Copyright (C) 2009 The Android Open Source Project
 #
@@ -121,7 +121,7 @@ def main(argv):
   results = list(set(perform_find(mindepth, prune, dirlist, filenames)))
   results.sort()
   for r in results:
-    print r
+    print(r)
 
 if __name__ == "__main__":
   main(sys.argv)