I've  got sound working on CentOS 7 VM ( connection  to console via virt-manager)
with slightly updated patch of Y.Kawada, self.type set "ich6".

+class LibvirtConfigGuestSound(LibvirtConfigGuestDevice):
+    def __init__(self, **kwargs):
+        super(LibvirtConfigGuestSound, self).__init__(root_name="sound",**kwargs)
+        self.type = "ich6"  # for Centos7
+        def format_dom(self):
+    dev = super(LibvirtConfigGuestSound, self).format_dom()
+        dev.set("model", self.type)
+        return dev

However, booting log of CentOS 7 VM contains :-
    Starting Manage Sound Card State (restore and store)...
    [[32m  OK  [0m] Started Manage Sound Card State (restore and store).
    [[32m  OK  [0m] Listening on RPCbind Server Activation Socket.