catch errors with unknown parser types
reuse the Stop() method when restarting the processinput plugin
Enforce a minimum run_interval of 1000 to prevent cases of 0 < run_interval < 1000 milliseconds
* changed the config to use a nested structure instead of an array of string arrays
* moved Directory config option into the cmd struct so that each stage can set it's own working directory
* added hostname and heka_pid