VMware Compute Driver Glance improvement

blueprint vmware-compute-driver

Glance change to fix image download to ESX
The current glance code downloads files in a blocking/synchronous
manner, the fix improves it to work with ESX glance file reader
in a non-blocking manner.
This allows ESX glance file reader to read items from the returned
queue.

Change-Id: I05ab7ac00878aeeea3bbcd7546b05398f2630dd3
Merge "VMware Compute Driver Glance improvement"