[vmware] disk is at thick mode always when creating vm

Description
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when I use a ovf image to create a vm, the disk mode is "thick" always. even I set disk_type of image as thin

Steps to reproduce
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1.create a ovf image
2.create a vm using the image

Expected result
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In vCenter, disk type of the vm is "thin" type

Actual result
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disk type of the vm is "thick" type

Environment
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Mitaka

Reason
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after calling import_app api of vCenter, nova-compute will post image to vCenter.
In fact, nova-compute should appoint size when calling import_app and use put method to commit url.
That's the way that vSphere client import ovf.