itertools.izip() is renamed to zip() in python3
itertools.izip() is renamed to zip() in python3

In python3, itertools.izip() was changed to zip(). Using six.zip() to
ensure the compatiblity between 2 and 3.

tianhao64/pyvmomi,Infinidat/pyvmomi,hartsock/pyvmomi,vmware/pyvmomi