Implement JSON encoder provided by pyvmomi

[abhi1693]

In several places, the code breaks due to issues with serialization. My setup utilizes salt-api which returns the data as a JSON object. Most functions are unable to serialize the data and crash.

Example: vmware_datacenter.get

This issue can be avoided by adding the JSON serializer provided by pyvmomi. It was implemented at https://github.com/vmware/pyvmomi/pull/732/files and works well