weldr: ensure a fresh dnf cache when making a new compose

dnf-json relies on dnf's ability to cache repository metadata. This is
important, because the API calls it quite often to serve requests for
package lists and depsolves.

However, osbuild's dnf stage always fetches new metadata, because it
doesn't have access to the host's cache. Since metadata is valid for
some time, even after a repository changed, the checksum we put in
the pipeline might be old.

Force a new metadata download when producing the pipeline. This is still
not perfect, but greatly reduces the probability of putting stale
metadata into the pipeline.

dnf-json

@@ -4,6 +4,7 @@ import datetime
 import dnf
 import hashlib
 import json
+import shutil
 import sys
 
 DNF_ERROR_EXIT_CODE = 10
@@ -35,9 +36,12 @@ def dnfrepo(desc, parent_conf=None):
     return repo
 
 
-def create_base(repos):
+def create_base(repos, clean=False):
     base = dnf.Base()
 
+    if clean:
+        shutil.rmtree(base.conf.cachedir, ignore_errors=True)
+
     for repo in repos:
         base.repos.add(dnfrepo(repo, base.conf))
 
@@ -79,7 +83,7 @@ command = call["command"]
 arguments = call.get("arguments", {})
 
 if command == "dump":
-    base = create_base(arguments.get("repos", {}))
+    base = create_base(arguments.get("repos", {}), arguments.get("clean", False))
     packages = []
     for package in base.sack.query().available():
         packages.append({
@@ -100,7 +104,7 @@ if command == "dump":
     }, sys.stdout)
 
 elif command == "depsolve":
-    base = create_base(arguments.get("repos", {}))
+    base = create_base(arguments.get("repos", {}), arguments.get("clean", False))
     errors = []
 
     try: