…are.

This is done by killing and respawning the jvms rather than reconnecting to existing
jvms, for a couple reasons. One is that it lets you restore tasks after server reboots
too, and another is that it lets you upgrade all the software on a box at once by just
restarting everything.

The main changes are,

1) Add "canRestore" and "stopGracefully" methods to Tasks that say if a task can
   stop gracefully, and actually do a graceful stop. RealtimeIndexTask is the only
   one that currently implements this.

2) Add "stop" method to TaskRunners that attempts to do an orderly shutdown.
   ThreadPoolTaskRunner- call stopGracefully on restorable tasks, wait for exit
   ForkingTaskRunner- close output stream to restorable tasks, wait for exit
   RemoteTaskRunner- do nothing special, we actually don't want to shutdown

3) Add "restore" method to TaskRunners that attempts to bootstrap tasks from last run.
   Only ForkingTaskRunner does anything here. It maintains a "restore.json" file with
   a list of restorable tasks.

4) Have the CliPeon's ExecutorLifecycle lock the task base directory to avoid a restored
   task and a zombie old task from stomping on each other.