worlddump: Use __future__ print_function

Commit e7361775c1 changed the code to
use Python 3 style print function, but when doing 'print()' in Python
2.7 it would print '()':
    >>> print()
    ()

Import the __future__ print function so that a blank line will be
printed as expected. This will now work the same in Python 2 & 3.

Change-Id: I61742e107278f2327c18c9ab0de52d1914f16c97

tools/worlddump.py

@@ -17,6 +17,8 @@
 
 """Dump the state of the world for post mortem."""
 
+from __future__ import print_function
+
 import argparse
 import datetime
 from distutils import spawn