Rules targetting docker-* are now built at runtime

* removed the macros `DOCKERFILE`, `TARGET`, & `DOCKER_TAG`
* introduced the macro `MAKE_DOCKER_BUILD_RULES`
* at runtime, `docker-*` are built from the `DISTROS` list: done using `eval` [1]
* `make help` is unchanged:

```
$ make | grep '\sdocker-'
make docker-alpine                                       Generate local docker images (Alpine)
make docker-alpine-dev                                   Generate local docker image (Alpine dev)
make docker-alpine-full                                  Generate local docker image (Alpine full)
make docker-alpine-minimal                               Generate local docker image (Alpine minimal)
make docker-ubuntu                                       Generate local docker images (Ubuntu)
make docker-ubuntu-dev                                   Generate local docker image (Ubuntu dev)
make docker-ubuntu-full                                  Generate local docker image (Ubuntu full)
make docker-ubuntu-minimal                               Generate local docker image (Ubuntu minimal)

$ make docker -n
docker buildx build --target full -f docker-files/alpine.Dockerfile -t glances:local-alpine-full .
docker buildx build --target minimal -f docker-files/alpine.Dockerfile -t glances:local-alpine-minimal .
docker buildx build --target dev -f docker-files/alpine.Dockerfile -t glances:local-alpine-dev .
docker buildx build --target full -f docker-files/ubuntu.Dockerfile -t glances:local-ubuntu-full .
docker buildx build --target minimal -f docker-files/ubuntu.Dockerfile -t glances:local-ubuntu-minimal .
docker buildx build --target dev -f docker-files/ubuntu.Dockerfile -t glances:local-ubuntu-dev .
```

[1] https://www.gnu.org/software/make/manual/html_node/Eval-Function.html

Signed-off-by: Ariel Otilibili <otilibil@eurecom.fr>

Author: ariel-anieli

Makefile

@@ -21,10 +21,6 @@ DOCKER_SOCK       ?= /var/run/docker.sock
 DOCKER_SOCKS      := -v $(PODMAN_SOCK):$(PODMAN_SOCK):ro -v $(DOCKER_SOCK):$(DOCKER_SOCK):ro
 DOCKER_OPTS       := --rm -e TZ="${TZ}" -e GLANCES_OPT="" --pid host --network host
 
-define DOCKER_TAG
-glances:local-$*
-endef
-
 # if the command is only `make`, the default tasks will be the printing of the help.
 .DEFAULT_GOAL := help
 
@@ -224,16 +220,12 @@ snapcraft:
 # Need Docker Buildx package (apt install docker-buildx on Ubuntu)
 # ===================================================================
 
-define DOCKERFILE
-docker-files/$(word 1,$(subst -, ,$*)).Dockerfile
-endef
-
-define TARGET
-$(word 2,$(subst -, ,$*))
+define MAKE_DOCKER_BUILD_RULES
+$($(DISTRO)_images): docker-$(DISTRO)-%: docker-files/$(DISTRO).Dockerfile
+	$(DOCKER_BUILD) --target $$* -f $$< -t glances:local-$(DISTRO)-$$* .
 endef
 
-$(DOCKER_IMAGES): docker-%:
-	$(DOCKER_BUILD) --target $(TARGET) -f $(DOCKERFILE) -t $(DOCKER_TAG) .
+$(foreach DISTRO,$(DISTROS),$(eval $(MAKE_DOCKER_BUILD_RULES)))
 
 docker: docker-alpine docker-ubuntu ## Generate local docker images
 
@@ -273,7 +265,7 @@ run-min-local-conf: ## Start minimal Glances in console mode with the system con
 	$(VENV_MIN)/python -m glances
 
 $(DOCKER_RUNTIMES): run-docker-%:
-	$(DOCKER_RUN) $(DOCKER_OPTS) $(DOCKER_SOCKS) -it $(DOCKER_TAG)
+	$(DOCKER_RUN) $(DOCKER_OPTS) $(DOCKER_SOCKS) -it glances:local-$*
 
 run-docker-alpine-minimal: ## Start Glances Alpine Docker minimal in console mode
 run-docker-alpine-full: ## Start Glances Alpine Docker full in console mode