Qtqa: Enable blacklisting of submodule update

In some cases we can't clone nested submodules. It seems to relate
to git version on CI nodes. Adding QtDeclarative to list to prevent
some manual tests to be cloned.

Change-Id: Idc0c5643a8e34225483bb4bdbae440c691331911
Reviewed-by: Tony Sarajärvi <tony.sarajarvi@digia.com>