qemuBlockGetNamedNodeData: Extract 'data_file_raw' flag

qemuBlockGetNamedNodeData: Extract 'data_file_raw' flag

The 'data_file_raw' flag of qcow2 notifies that all data inside the
'data_file' is a raw image so can be used standalone without the
metadata without any problem (except for not updating the dirty
bitmaps).

Our migration safety checks will allow skipping the migration safety
check for these files as during migration we know it's safe to re-create
this on the destination in a location that isn't shared.

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