Fixes cinder-volume service startup on Windows

The Windows service fails due to missing non-blocking IO features
in eventlet. This fix adds a conditional path on Windows to execute
the service accordingly.

This bug had already been fixed by this this commit:
https://review.openstack.org/#/c/44744/ but it had been reverted
here, causing the Windows service to fail again
https://review.openstack.org/67031

Fixes bug: #1219896

Change-Id: I46c6b332e614b6a84ec8372dbec3ee9fb09336de
Merge "Fixes cinder-volume service startup on Windows"