Fix: 'change_key' of current patchset pushed by 'refs/changes' is still old one.

When an existing Change's current patchset is replaced by another commit pushed by
'refs/changes', in the DB Change table the related record's 'change_key' is NOT
updated accordingly.

This commit fix it to make the related DB record to be consistant with that in
Git repository.

Change-Id: I5a34748246c0f6783f23852f87c055081dbb67d3
1 file changed