The export process now exports the VM directly from the build directory
into the output directory. There are no intermediate steps or copying of
files involved. This means that there is no longer any benefit in having
a separate directory to house the VHD files - see #5206 for the
reasoning behind the introduction of this feature.
If a user wishes to house the build files on a separate disk from the
output directory (perhaps for performance reasons or due to disk space
limitations) they can still do so through the use of `temp_path`.
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