test 'Iso8601' is properly deserializing dates.

Deliberately exercises the code in Iso8601 used by
VmomiSupport.py to validate that the import for
datetime reading is working as expected.

related to: https://github.com/vmware/pyvmomi/issues/112
python3: fix Iso8601 import statement

The import statement for Iso8601 was not properly
updated. This fix changes the import statement so
it works properly after python3 support changes.

fixes https://github.com/vmware/pyvmomi/issues/112