docker: Do not run tests in 'intermediate' images

We can still build the DOCKER_INTERMEDIATE_IMAGES images,
but they won't appear in 'make test*@$IMAGE'.

Signed-off-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Signed-off-by: Alex Bennée <alex.bennee@linaro.org>

tests/docker/Makefile.include

@@ -5,6 +5,8 @@
 DOCKER_SUFFIX := .docker
 DOCKER_FILES_DIR := $(SRC_PATH)/tests/docker/dockerfiles
 DOCKER_DEPRECATED_IMAGES := debian
+# we don't run tests on intermediate images (used as base by another image)
+DOCKER_INTERMEDIATE_IMAGES := debian8 debian9 debian8-mxe debian-ports debian-sid
 DOCKER_IMAGES := $(filter-out $(DOCKER_DEPRECATED_IMAGES),$(sort $(notdir $(basename $(wildcard $(DOCKER_FILES_DIR)/*.docker)))))
 DOCKER_TARGETS := $(patsubst %,docker-image-%,$(DOCKER_IMAGES))
 # Use a global constant ccache directory to speed up repetitive builds
@@ -98,7 +100,7 @@ docker-image-travis: NOUSER=1
 docker-image-tricore-cross: docker-image-debian9
 
 # Expand all the pre-requistes for each docker image and test combination
-$(foreach i,$(DOCKER_IMAGES) $(DOCKER_DEPRECATED_IMAGES), \
+$(foreach i,$(filter-out $(DOCKER_INTERMEDIATE_IMAGES),$(DOCKER_IMAGES) $(DOCKER_DEPRECATED_IMAGES)), \
 	$(foreach t,$(DOCKER_TESTS) $(DOCKER_TOOLS), \
 		$(eval .PHONY: docker-$t@$i) \
 		$(eval docker-$t@$i: docker-image-$i docker-run-$t@$i) \