Hooked stream_metadata(..) with chown(..).

Part of #3687. So far, only chown(..) in user-stream-wrapper has been hooked with stream_metadata(..) function. Similar to commit 1f55a08.

Also passes vfsStream's chownChangesUser test case.
@kevinxucs: I think I missed this in f87415ef4b2fe1bf30e949cf21c8015ccab4084e, do you want to send PR? Also chgrp (and maybe some other as well?) may be fixed.