Create .changes files for reproducible builds

release rpm files currently do not have .changes files, but these are
needed to extract SOURCE_DATE_EPOCH for reproducible builds.

Using the time stamp of the last commit to any of the input, which is
the 000package-groups and 000update-repos source package, as the time
for the changes entry would be reproducible, however there is resistance
to that.

The other date that is related is the time of the last
source change for any input to the whole distribution, however AFAIK
this date is not cheap enough to compute for OBS-VCS. This hopefully
changes once we move to git.

However to not delay making progress with reproducible builds in
Factory, I propose this change which makes the output of this script
non-reproducible, by using the current wall-clock time. But only when
this script produced a change to be commited. The release binary rpms
will still be reproducible. We can revisit making the generated source
reproducible, later.

See https://reproducible-builds.org/ for more general information on
this topic.

pkglistgen/tool.py

@@ -8,6 +8,8 @@ import shutil
 import subprocess
 import yaml
 
+from datetime import datetime, timezone
+
 from typing import Any, Mapping, Optional
 
 from lxml import etree as ET
@@ -743,6 +745,22 @@ class PkgListGen(ToolBase.ToolBase):
 
         file_utils.multibuild_from_glob(release_dir, '*.spec')
         self.build_stub(release_dir, 'spec')
+
+        todo_spec_files = []
+        package = Package(release_dir)
+        if package.get_status(False, ' '):
+            todo_spec_files = glob.glob(os.path.join(release_dir, '*.spec'))
+        for spec_file in todo_spec_files:
+            changes_file = os.path.splitext(spec_file)[0] + '.changes'
+            with open(changes_file, 'w', encoding="utf-8") as f:
+                date = datetime.now(timezone.utc)
+                date = date.strftime("%a %b %d %H:%M:%S %Z %Y")
+                f.write(
+                    "-------------------------------------------------------------------\n"
+                    + date + " - openSUSE <packaging@lists.opensuse.org>\n\n"
+                    "- automatically generated by openSUSE-release-tools/pkglistgen\n\n"
+                )
+
         self.commit_package(release_dir)
 
         if only_release_packages: