Fixes cinder error state volume delete on Windows

If the volume creation fails and the iSCSI disk is not created,
trying to delete the error state volume will fail on Windows.

Deleting the iSCSI disk must be skipped when it does not exist.

Change-Id: I2cd615e71fe457c241bea207c4bd8904c1ffd9cb
Closes-Bug: #1304516
Merge "Fixes cinder error state volume delete on Windows"