VMware: Usng RetrvProprtisEx & does multi ESX scan

VMware: Usng RetrvProprtisEx & does multi ESX scan

The existing code uses deprecated API RetrieveProperties for querying through
property collector. The public doc asks to use RetrievePropertiesEx instead.

RetrievePropertiesEx works by retrieving results in serveral batches rather than
retrieval in a single API call. This works well in environments containing
large number of VMs or ESX hosts.

There are three steps involved 1. Get first batch 2. Continue retrieving using
a token 3. Cancel retrieval when not needed

Batch size is user configurable, default is 100 results per batch.

The review also fixes a careless programming error leading to scanning only
1 ESX host under the vCenter server for datastores.

Fixes bug: 1227078
Fixes bug: 1229654
DocImpact

Change-Id: I85a6f6a7e2d764b9843efbd0dd347fba3ef19310