/admin/logging handler should be able to configure logs on all nodes

The LoggingHandler registered at /admin/logging can configure log levels for the current node. This is nice but in SolrCloud, what's needed is an ability to change the level for all nodes in the cluster. I propose that this be a parameter name "distrib" defaulting to SolrCloud mode's status. An admin UI could have a checkbox for it. I don't propose that the read operations be changed – they can continue to just look at the node you are hitting.