Open Stack

Hi, Michael and all,

	I created some changes to config_drive, and hope to get some feedback. The patches are at https://review.openstack.org/#/q/status:open+project:openstack/nova+branch:master+topic:config_drive_cleanup,n,z 

	The basically ideas of the changes are:
	1) Instead of using host based config option to decide config_drive and config_drive_format, fetch such information from image property. Accordingly to Michael, its image that decide if it need config drive, and I think it's image that decide what's the config drive format supported. (like cloudinit verion 1.0 does not support iso9660 format. (http://cloudinit.readthedocs.org/en/latest/topics/datasources.html#version-1)

	2) I noticed some virt drivers like VMWare/hyperv support only iso9660 format, , thus select the host based on image property, for example, if a host can't support vfat, don't try to schedule a server requires 'vfat' to that host.

	The implementation detais are:

	1) Image can provide two properties, 'config_drive' and 'config_drive_format'.

	2) There is a cloud wise force_config_drive option (in the api service) to decide if the config_drive will be forced applied.

	3) There is a host specific config_drive_format to set the default config_drive format if not specified in the image property.

	4) In the image property filter, we will select the host that support the config_drive_format in image property

	Any feedback is welcome to these changes.

Thanks
--jyh