Disable chef client at the end of a run.

Nasty kludge to disable chef-client at the end of a successful run A safety measure to stop auto recheffing. Recheffing has caused problems when solr dies on the chef server, causing get_head_nodes to return a reduced subset of actual headnodes, causing mysql to get split brain. 

*This is not intended to be a long term fix.* The proper way to do this is to bail of chef-solr is fudged.