make a call to solrnode/admin/cores with the given params and give a callback. This is designed to be
asynchronous because the system would want to batch the calls made to any given node
params - The params to be passed to the Snitch counterpart
klas - The name of the class to be invoked in the remote node
callback - The callback to be called when the response is obtained from remote node.
If this is passed as null the entire response map will be added as tags