Session timeouts cause PropertyCollector to return empty data

[hartsock]

Sessions that time out and then invoke a method on the vim.PropertyCollector object class can appear to execute the method without error and yield erroneous empty data. This makes it difficult for developers on working on products with long-running processes to distinguish between a session timeout error and a legitimate 'None' response from the server.

We need a fix for this issue that can properly handle session timeouts and we need this fixed by the next release.