Convert generate-self-extracting-archive.py to python 3

Test: Add a VENDOR_BLOBS_LICENSE entry to an existing product, then `m with-license`
Bug: 203436762
Change-Id: I4bbe77bda7789b6c44bea141518b1cd2e699d326
diff --git a/tools/generate-self-extracting-archive.py b/tools/generate-self-extracting-archive.py
index 5b0628d..c9f56cb 100755
--- a/tools/generate-self-extracting-archive.py
+++ b/tools/generate-self-extracting-archive.py
@@ -1,4 +1,4 @@
-#!/usr/bin/env python
+#!/usr/bin/env python3
 #
 # Copyright (C) 2019 The Android Open Source Project
 #
@@ -120,7 +120,7 @@
 
 def main(argv):
   if len(argv) != 5:
-    print 'generate-self-extracting-archive.py expects exactly 4 arguments'
+    print('generate-self-extracting-archive.py expects exactly 4 arguments')
     sys.exit(1)
 
   output_filename = argv[1]
@@ -134,11 +134,11 @@
     license = license_file.read()
 
   if not license:
-    print 'License file was empty'
+    print('License file was empty')
     sys.exit(1)
 
   if 'SOFTWARE LICENSE AGREEMENT' not in license:
-    print 'License does not look like a license'
+    print('License does not look like a license')
     sys.exit(1)
 
   comment_line = '# %s\n' % comment