ci/overrides.py: use stderr for logging

Some commands are designed to output parseable data on stdout. Let's
consistently use stderr for informational output.

ci/overrides.py

@@ -206,7 +206,7 @@ def get_manifest_packages(arch):
     versions = [b['id'] for b in get_build_list() if arch in b['arches']]
     if not versions:
         return {}
-    print(f'Reading generated lockfile from build {versions[0]} on {arch}')
+    eprint(f'Reading generated lockfile from build {versions[0]} on {arch}')
     lockfile_url = GENERATED_LOCKFILE_URL_TEMPLATE.format(stream=get_stream(),
             version=versions[0], arch=arch)
     resp = requests.get(lockfile_url)
@@ -272,12 +272,12 @@ def setup_repos(base, treefile):
     for repo in base.repos.values():
         repo.disable()
 
-    print("Enabled repos:")
+    eprint("Enabled repos:")
     for repo in treefile['repos']:
         base.repos[repo].enable()
-        print(f"- {repo}")
+        eprint(f"- {repo}")
 
-    print("Downloading metadata")
+    eprint("Downloading metadata")
     base.fill_sack(load_system_repo=False)
 
 
@@ -316,13 +316,13 @@ def graduate_lockfile(base, fn):
         if not graduated:
             new_packages[name] = lock
         else:
-            print(f"{fn}: {nevra} has graduated")
+            eprint(f"{fn}: {nevra} has graduated")
 
     if lockfile['packages'] != new_packages:
         lockfile['packages'] = new_packages
         write_lockfile(fn, lockfile)
     else:
-        print(f"{fn}: no packages graduated")
+        eprint(f"{fn}: no packages graduated")
 
 
 def sack_has_nevra_greater_or_equal(base, nevra):
@@ -334,7 +334,7 @@ def sack_has_nevra_greater_or_equal(base, nevra):
         # Odd... the only way I can imagine this happen is if we fast-track a
         # brand new package from Koji which hasn't hit the updates repo yet.
         # Corner-case, but let's be nice.
-        print(f"couldn't find package {nevra.name}; assuming not graduated")
+        eprint(f"couldn't find package {nevra.name}; assuming not graduated")
         return False
 
     nevra_latest = hawkey.split_nevra(str(pkgs[0]))
@@ -375,5 +375,9 @@ def check_dist_tag(name, info, dist):
         raise Exception(f"Package {name}-{info['evra']} doesn't match expected dist tag {dist}")
 
 
+def eprint(*args, **kwargs):
+    print(*args, file=sys.stderr, **kwargs)
+
+
 if __name__ == "__main__":
     sys.exit(main())