Second try to fix LUVerifyCluster

My previous patch, commit 785d142e, fixed the case where a node is marked
offline. With this patch it'll also handle other failures correctly.

 * Hooks Results
   - ERROR: node node2.example.com: Communication failure in hooks
   execution: Connection failed (111: Connection refused)

Signed-off-by: Michael Hanselmann <hansmi@google.com>
Reviewed-by: Iustin Pop <iustin@google.com>