test: rename mpp-*.json to *.mpp.json

This simplifies the `test-data` rules in `Makefile` considerably. Also,
it allows adding `*.mpp.json` files in other directories without needing
to copy rules. (make's pattern-based rules only allow a single `%`).

Adjust test/data/README.md accordingly.

Makefile

@@ -205,10 +205,10 @@ coverity-clean-all: coverity-clean
 # for linters and other tests on the source code.
 #
 
-TEST_MANIFESTS_MPP = $(wildcard $(SRCDIR)/test/data/manifests/mpp-*.json)
-TEST_MANIFESTS_GEN = $(patsubst $(SRCDIR)/test/data/manifests/mpp-%.json,$(SRCDIR)/test/data/manifests/%.json,$(TEST_MANIFESTS_MPP))
+TEST_MANIFESTS_MPP = $(wildcard $(SRCDIR)/test/data/manifests/*.mpp.json)
+TEST_MANIFESTS_GEN = $(TEST_MANIFESTS_MPP:%.mpp.json=%.json)
 
-$(TEST_MANIFESTS_GEN): $(SRCDIR)/test/data/manifests/%.json: $(SRCDIR)/test/data/manifests/mpp-%.json
+$(TEST_MANIFESTS_GEN): %.json: %.mpp.json
 	$(SRCDIR)/tools/mpp-depsolve.py <"$<" \
 		| $(SRCDIR)/tools/mpp-import-pipeline.py >"$@" \
 			"--cwd=$(SRCDIR)/test/data/manifests"

test/data/README.md

@@ -32,10 +32,10 @@ do not allow comments, this file shortly describes their purpose.
    this manifest's tree is constructed just from the filesystem package and is
    marked using the selinux stage.
 
-   Manifests prefixed with `mpp-*` are fed through the ManifestPreProcessors and
-   then stored in the same directory with the `mpp-*` prefix dropped. The
-   generated files are committed to the repository. Nevertheless, if you need to
-   regenerate them, use `make test-data`.
+   Manifests ending on `.mpp.json` are fed through the ManifestPreProcessors
+   and then stored in the same directory with an `.json` extension (replacing
+   `.mpp.json`). generated files are committed to the repository. Nevertheless,
+   if you need to regenerate them, use `make test-data`.
 
  * `./sources/`:
    This directory contains test-data for runtime tests of the source-engines. It