qemu: test NBD command-line builder and parser

Enable more testing of NBD parsing, to ensure rewrites work.
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>
Signed-off-by: NEric Blake <eblake@redhat.com>

tests/qemuxml2xmltest.c

@@ -169,6 +169,7 @@ mymain(void)
     DO_TEST("disk-drive-cache-v1-wt");
     DO_TEST("disk-drive-cache-v1-wb");
     DO_TEST("disk-drive-cache-v1-none");
+    DO_TEST("disk-drive-network-nbd");
     DO_TEST("disk-scsi-device");
     DO_TEST("disk-scsi-vscsi");
     DO_TEST("disk-scsi-virtio-scsi");