Currently if CONTAINER_TECH=nspawn is uses, Cinder and Swift
are unable to create volumes as space is fully allocated for
machines volume.
This shrinks machine00 mount to 8192 to make space for Cinder
and Swift volumes when using nspawn for the container tech.
Change-Id: Ief0040f638f0d3570557ac76fd5e0a8aee80df8d