This patch adds the Hyper-V 'vhdx' disk format to the Glance
configuration. This allows users to upload 'vhdx' images by default.
'vhdx' disks can have much larger storage capacity than the older 'vhd'
format [1]. (Plus, anything with 'x' in the name is awesome.)
DocImpact: Docs will need to be updated to indicate that the 'vhdx'
disk_format is now one of the default disk formats supported by Glance.
UpgradeImpact: Adds 'vhdx' to the default list of disk_formats. Operators
will no longer need to configure specifically to use 'vhdx' disks.
[1] https://technet.microsoft.com/en-us/library/hh831446(v=ws.11).aspx
Spec-Lite: https://review.openstack.org/#/c/347626
Change-Id: I4e172c78d7afeb8be5a0123238efe3d8e4b044c9
fc0b47beb6