Avoid using the disk cache on volume initialisation

When caching is involved, the volume might be
unmapped before the copy actually hit the disk or the
VM starts booting before all of the data has been flushed,
which causes the VM to crash at an arbitrary point in time.

Closes-Bug: #1363016

Change-Id: I7a04f683add8c23b9125fe837c4048ccc3ac224d
Merge "Avoid using the disk cache on volume initialisation"