pillar/Makefile: fix $(shell ) build-docker-test

$(shell ...) is evaluated immediately and not on the line
it is executed on, therefore build-docker-test needs to be
split into three different targets

otherwise an error message like this shows up:
```
Dockerfile:19
--------------------
  17 |
  18 |     FROM ${REL_HASH_LFEDGE_EVE_UEFI} AS uefi-build
  19 | >>> FROM ${REL_HASH_LFEDGE_EVE_DOM0_ZTOOLS} AS zfs
  20 |     RUN mkdir /out
  21 |     # copy zfs-related files from dom0-ztools using prepared list of files
--------------------
ERROR: failed to build: failed to solve: lfedge/eve-dom0-ztools:000adaabe42b4f34dc196b722f143d3ae39f47fa-dirty-cb3d84e: failed to resolve source metadata for docker.io/lfedge/eve-dom0-ztools:000adaabe42b4f34dc196b722f143d3ae39f47fa-dirty-cb3d84e: docker.io/lfedge/eve-dom0-ztools:000adaabe42b4f34dc196b722f143d3ae39f47fa-dirty-cb3d84e: not found
```

Signed-off-by: Christoph Ostarek <[email protected]>

Author: christoph-zededa

pkg/pillar/Makefile

@@ -10,6 +10,7 @@ ZARCH         ?= $(HOSTARCH)
 DISTDIR       := dist/$(ZARCH)
 BUILD_VERSION ?=
 
+DOCKER_LIKE_LKT:= ../../build-tools/bin/linuxkit pkg build --network --platforms linux/$(ZARCH) --dry-run --force ./ | tail -n1 | perl -pe 's/ buildx / /g'
 DOCKER_TAG:=lfedge/eve-pillar:local-$(ZARCH)
 
 APPS = zedbox
@@ -66,18 +67,18 @@ $(APPS1): $(DISTDIR)
 shell:
 	make -C ../.. shell
 
-build-docker build-docker-test: DOCKER_LIKE_LKT = $(shell ../../build-tools/bin/linuxkit pkg build --network --platforms linux/$(ZARCH) --dry-run --force ./ | tail -n1 | perl -pe 's/ buildx / /g')
-
 build-docker:
-	$(DOCKER_LIKE_LKT) -t $(DOCKER_TAG)
+	$(shell $(DOCKER_LIKE_LKT)) -t $(DOCKER_TAG)
 
 enter-docker-dev: build-docker-test
 	docker run --platform linux/$(ZARCH) -it --rm --entrypoint /bin/sh $(DOCKER_TAG)
 
-build-docker-test:
+build-docker-test-dependencies:
 	make -C ../../ pillar-cache-export-docker-load
-	$(DOCKER_LIKE_LKT) --build-arg TEST_TOOLS=y --load --target build
-	docker image tag $(shell $(DOCKER_LIKE_LKT) --build-arg TEST_TOOLS=y --load -q --target build) $(DOCKER_TAG)
+build-docker-test-build: build-docker-test-dependencies
+	$(shell $(DOCKER_LIKE_LKT)) --build-arg TEST_TOOLS=y --load --target build
+build-docker-test: build-docker-test-build
+	docker image tag $(shell $(shell $(DOCKER_LIKE_LKT)) --build-arg TEST_TOOLS=y --load -q --target build) $(DOCKER_TAG)
 
 test: build-docker-test
 	rm -f results.json