Disk QoS is not available on versions prior to WS 2012 R2.
Because of this and the fact that the driver attempts to set IOPS
limits even if those are not specified, spawning instances currently
fails when using previous HyperV versions.
This patch fixes the issues by skipping setting QoS specs when
this feature is not supported, logging a warning.
Closes-Bug: #1463317
Change-Id: I086f3a034ffcc56a09a5ecf3e9a142cc86e67c41