archive creation start/end timestamp: use utc

the timestamp given via cli is already expected to be utc.

the timestamp which is automatically created when no cli timestamp is given is also utc.

thus, also use utc for .start and .end.

borg/archive.py

@@ -128,7 +128,7 @@ class Archive:
     def __init__(self, repository, key, manifest, name, cache=None, create=False,
                  checkpoint_interval=300, numeric_owner=False, progress=False,
                  chunker_params=CHUNKER_PARAMS,
-                 start=datetime.now(), end=datetime.now()):
+                 start=datetime.utcnow(), end=datetime.utcnow()):
         self.cwd = os.getcwd()
         self.key = key
         self.repository = repository

borg/archiver.py

@@ -191,7 +191,7 @@ class Archiver:
                 if args.progress:
                     archive.stats.show_progress(final=True)
                 if args.stats:
-                    archive.end = datetime.now()
+                    archive.end = datetime.utcnow()
                     log_multi(DASHES,
                               str(archive),
                               DASHES,
@@ -202,7 +202,7 @@ class Archiver:
         self.output_filter = args.output_filter
         self.output_list = args.output_list
         dry_run = args.dry_run
-        t0 = datetime.now()
+        t0 = datetime.utcnow()
         if not dry_run:
             repository = self.open_repository(args, exclusive=True)
             manifest, key = Manifest.load(repository)