diskSize defaults to the previous hard-coded 8192:
no change for existing users.
Users can set diskSize when building images which require
larger disk space; thus avoiding the error:
ERROR: cptofs failed. diskSize might be too small for closure.
Signed-off-by: Sirio Balmelli <sirio@b-ad.ch>
Co-authored-by: superherointj <5861043+superherointj@users.noreply.github.com>