tests/vm: move images to $HOME/.cache/qemu-vm/images

It's easier to move around the images then, by replacing the
subdirectory with a symlink.  Allows to share the images between
multiple qemu checkouts for example.
Signed-off-by: NGerd Hoffmann <kraxel@redhat.com>
Reviewed-by: NPhilippe Mathieu-Daudé <philmd@redhat.com>
Tested-by: NPhilippe Mathieu-Daudé <philmd@redhat.com>
Signed-off-by: NAlex Bennée <alex.bennee@linaro.org>

tests/vm/Makefile.include

@@ -3,7 +3,8 @@
 .PHONY: vm-build-all vm-clean-all
 
 IMAGES := ubuntu.i386 freebsd netbsd openbsd centos
-IMAGE_FILES := $(patsubst %, tests/vm/%.img, $(IMAGES))
+IMAGES_DIR := $(HOME)/.cache/qemu-vm/images
+IMAGE_FILES := $(patsubst %, $(IMAGES_DIR)/%.img, $(IMAGES))
 
 .PRECIOUS: $(IMAGE_FILES)
 
@@ -24,9 +25,10 @@ vm-build-all: $(addprefix vm-build-, $(IMAGES))
 vm-clean-all:
 	rm -f $(IMAGE_FILES)
 
-tests/vm/%.img: $(SRC_PATH)/tests/vm/% \
-		$(SRC_PATH)/tests/vm/basevm.py \
-		$(SRC_PATH)/tests/vm/Makefile.include
+$(IMAGES_DIR)/%.img:	$(SRC_PATH)/tests/vm/% \
+			$(SRC_PATH)/tests/vm/basevm.py \
+			$(SRC_PATH)/tests/vm/Makefile.include
+	@mkdir -p $(IMAGES_DIR)
 	$(call quiet-command, \
 		$< \
 		$(if $(V)$(DEBUG), --debug) \
@@ -37,7 +39,7 @@ tests/vm/%.img: $(SRC_PATH)/tests/vm/% \
 
 
 # Build in VM $(IMAGE)
-vm-build-%: tests/vm/%.img
+vm-build-%: $(IMAGES_DIR)/%.img
 	$(call quiet-command, \
 		$(SRC_PATH)/tests/vm/$* \
 		$(if $(V)$(DEBUG), --debug) \