test-swift-log-upload: fix dry_run parameter

This was pointed out and fixed by jhesketh in
Ie4888606a8ca4ffe2eb99ddbbcd9d5cee8ceec44, but I forgot to add it to
the test role.  Sure enough, it fails as jhesketh predicted.

[1] https://review.opendev.org/#/c/592929/3..4/roles/upload-logs-swift/library/zuul_swift_upload.py

Change-Id: I8d25a234fb92cd1bcfcd0cb7ddf9b8222dbd5978

roles/test-upload-logs-swift/library/zuul_swift_upload.py

@@ -649,8 +649,8 @@ class Uploader():
     def __init__(self, cloud, container, prefix=None, delete_after=None,
                  public=True, dry_run=False):
 
+        self.dry_run = dry_run
         if dry_run:
-            self.dry_run = True
             self.url = 'http://dry-run-url.com/a/path/'
             return