tests/vm: Take the J=x setting into account for the vm-boot-ssh targets, too

For testing whether the VMs can deal with multiple CPUs correctly,
it is useful to be able to use the "J=<cpus>" setting for the
vm-boot-ssh targets, too.

Message-Id: <20190726100207.19112-1-thuth@redhat.com>
Signed-off-by: Thomas Huth <thuth@redhat.com>

tests/vm/Makefile.include

@@ -80,6 +80,7 @@ vm-boot-serial-%: $(IMAGES_DIR)/%.img
 vm-boot-ssh-%: $(IMAGES_DIR)/%.img
 	$(call quiet-command, \
 		$(SRC_PATH)/tests/vm/$* \
+		$(if $(J),--jobs $(J)) \
 		--image "$<" \
 		--interactive \
 		false, \