Make unpack.py compatible with Python 3

Change-Id: I55a0b0f4fa0e9bf24650bf72efbed25142c5b2d0
diff --git a/unpack.py b/unpack.py
index 0d376b8..5d29c9d 100755
--- a/unpack.py
+++ b/unpack.py
@@ -1,4 +1,4 @@
-#!/usr/bin/env python2.7
+#!/usr/bin/env python3
 
 """Unpacks a prebuilt to look like an Android build directory."""
 
@@ -24,14 +24,14 @@
     adb_source_path = pristine_dir + "/adb"
     # Make sure the relevant files are here - currently just adb + target files.
     if not os.path.isfile(adb_source_path):
-        print "ADB missing from prebuilt"
+        print("ADB missing from prebuilt")
         sys.exit(1)
 
     # Make sure we have exactly one target zip
     target_files_search = pristine_dir + "/qemu_trusty_arm64-target_files-*.zip"
     target_files_zip_glob = glob.glob(target_files_search)
     if not target_files_zip_glob:
-        print "No Android target_files found"
+        print("No Android target_files found")
         sys.exit(1)
     if len(target_files_zip_glob) > 1:
         print ("Multiple Android target_files archives found. Please clean up "