JettyBugMonitor thread should kill TT if can't find jetty selector thread

We ran into a case where a tasktracker started but for some reason the jetty thread didn't start or died shortly after start. I couldn't find anything useful as to why.

Since Jetty wasn't running the TT couldn't serve up any map output. The JettyBugMonitor thread saw this but just spit out the warning. We should have it just kill the TT since its basically unusable without it.

> 2012-07-23 05:42:04,072 WARN org.apache.hadoop.mapred.JettyBugMonitor: Could
not locate Jetty selector threads