Hyper-V:Preserve config drive image after the instance is resized

If we configure config_drive_cdrom=True in nova.conf,
the config drive image will be lost after the instance
is resized on hyperV. This is because nova compute will
not copy the disk file if the file's ResourceSubType
is not 'Virtual Hard Disk'.

This commit adds 'Virtual CD/DVD Disk' into disk_resources
to preserve the config drive image after the instance is
resized.

Closes-Bug: #1250324

Change-Id: Ia125a8b132d194ddc2230754fd1b813698b410a8
Merge "Hyper-V:Preserve config drive image after the instance is resized"