Comment 9 for bug 1996188

Code LGTM. I do have a concern about the config opt, namely, that the default is

  vmdk_allowed_types = ['streamOptimized', 'monolithicSparse']

and if you set it like this:

  vmdk_allowed_types = [ ]

The behavior is "allow all" ... which the help text mentions, but I think this is very easy to mis-configure, because if you only want 'streamOptimized' you remove 'monolithicSparse' from the list, and following that logic, if you don't want any, you'll remove 'streamOptimized' too ... but the behavior will be the exact opposite of what you expect. So I'd prefer an empty list mean "don't allow any".

The downside is that if someone does want to allow all possible formats, they'll have to list them all. Or we could introduce a sentinel value like 'vmdk_allowed_types_ANY'

  vmdk_allowed_types = ['vmdk_allowed_types_ANY']

and hope that vmware doesn't introduce a 'vmdk_allowed_types_ANY' subformat.

But the other upside of [] == "none" is that use of vmdk can be turned off in Nova without having to depend on the disk_formats setting in Glance. It would also handle the problem of existing vmdks in deployments that don't actually use vmdk, but are using the default disk_formats value in Glance (which includes vmdk).