qemu: domain: Check few more fields for when changing disk source

qemu: domain: Check few more fields for when changing disk source

Both disk->src->shared and disk->src->readonly can't be modified when
changing disk source for floppy and cdrom drives since both arguments
are passed as arguments of the disk rather than the image in qemu.

Historically these fields have only two possible values since they are
represented as XML thus we need to ignore if user did not provide them
and thus we are treating them as false.