Fix unicode in "virtual_machine_device_info" (#382)
Fix unicode in "virtual_machine_device_info" (#382)

When format a string with the info of virtual machine which contains
unicode string, it would raise UnicodeEncodeError.
We cloud explict the unicode string type to avoid that exception.

Close-Issue: #150
jm66/pyvmomi-community-samples,vmware/pyvmomi-community-samples,prziborowski/pyvmomi-community-samples,pathcl/pyvmomi-community-samples