Enable setting DummySiteinfo content dict directly

- may be used by dry_site_tests e.g.
  see I968e1faad475b0c4d9ebfa6730a8d03ada6fe58a
  or examples

Change-Id: I5d8790c9b1ab11d00280ca66f9a729ec3cf44054
Merge "Enable setting DummySiteinfo content dict directly"