Support 'make osv.vmdk' without 'make all'

Add 'all' as dependent target of osv.vmdk/.vdi, to prevent build error.

Signed-off-by: Takuya ASADA <syuu@cloudius-systems.com>
Signed-off-by: Pekka Enberg <penberg@cloudius-systems.com>

Makefile

@@ -42,7 +42,7 @@ check: export image ?= tests
 check: all
 	./scripts/test.py
 
-osv.vmdk osv.vdi:
+osv.vmdk osv.vdi: all
 	$(MAKE) -r -C $(dir $(submake)) $@
 .PHONY: osv.vmdk osv.vdi