conf: domain: Output 'format' attribute of '<nvram>' also for' raw images

conf: domain: Output 'format' attribute of '<nvram>' also for' raw images

As the 'format' field is meant to carry the format of the nvram image we
should output it even when the image is 'raw'.

Currently this is not a problem but later patches will allow mismatch
between the nvram format and loader format (as nothing really
technically requires them to be the same and this then could become
problem).

Modify the condition and update tests.

Signed-off-by: Peter Krempa <pkrempa@redhat.com>
Reviewed-by: Michal Privoznik <mprivozn@redhat.com>
Reviewed-by: Ján Tomko <jtomko@redhat.com>