Update for Splunk 6

All dashboards have been rebuilt using Splunk 6 Simple XML.

Host dropdowns now key into |metadata for significantly improved
responsiveness

Dashboards have been retooled to take advantage of search
post-processing, reducing the number of searches triggered
significantly, and thus greatly improving performance.

Removed 'error_host' extract from props.conf, as it appeared to be
non-functional.  jmx_connectivity_errors.xml now simply uses host.