qemu-nbd is already provided by subpackage qemu-img, so we don't need to
install qemu package.

--- a/alpine-make-vm-image
+++ b/alpine-make-vm-image
@@ -320,7 +320,7 @@
 if [ "$INSTALL_HOST_PKGS" = yes ]; then
 	einfo 'Installing needed packages on host system'
 
-	_apk add -t $VIRTUAL_PKG qemu qemu-img
+	_apk add -t $VIRTUAL_PKG qemu-img
 	install_fs_tools "$ROOTFS"
 fi
 
