rpm: Change default diff format to block, from diff
rpm: Change default diff format to block, from diff

tmp-user/rpm-ostree,giuseppe/rpm-ostree,mdshuai/rpm-ostree,mdshuai/rpm-ostree,tmp-user/rpm-ostree,giuseppe/rpm-ostree,giuseppe/rpm-ostree,tmp-user/rpm-ostree,mdshuai/rpm-ostree,mdshuai/rpm-ostree,giuseppe/rpm-ostree,tmp-user/rpm-ostree