virsh: Register and unregister the close callback also in cmdConnect

This patch improves the error message after disconnecting from the
hypervisor and adds the close callback operations required not to leak
the callback reference.
(cherry picked from commit 69ab0756)

tools/virsh.c

@@ -391,10 +391,14 @@ cmdConnect(vshControl *ctl, const vshCmd *cmd)
 
     if (ctl->conn) {
         int ret;
-        if ((ret = virConnectClose(ctl->conn)) != 0) {
-            vshError(ctl, _("Failed to disconnect from the hypervisor, %d leaked reference(s)"), ret);
-            return false;
-        }
+
+        virConnectUnregisterCloseCallback(ctl->conn, vshCatchDisconnect);
+        ret = virConnectClose(ctl->conn);
+        if (ret < 0)
+            vshError(ctl, "%s", _("Failed to disconnect from the hypervisor"));
+        else if (ret > 0)
+            vshError(ctl, "%s", _("One or more references were leaked after "
+                                  "disconnect from the hypervisor"));
         ctl->conn = NULL;
     }
 
@@ -411,10 +415,16 @@ cmdConnect(vshControl *ctl, const vshCmd *cmd)
     ctl->conn = virConnectOpenAuth(ctl->name, virConnectAuthPtrDefault,
                                    ctl->readonly ? VIR_CONNECT_RO : 0);
 
-    if (!ctl->conn)
+    if (!ctl->conn) {
         vshError(ctl, "%s", _("Failed to connect to the hypervisor"));
+        return false;
+    }
+
+    if (virConnectRegisterCloseCallback(ctl->conn, vshCatchDisconnect,
+                                        NULL, NULL) < 0)
+        vshError(ctl, "%s", _("Unable to register disconnect callback"));
 
-    return !!ctl->conn;
+    return true;
 }