Rescheduled event execution on fail (not on reload)

[dreh23]

This is related to #30

If a plugin fails for some reason - shotguneventDaemon should retry executing the plugin after an amount of time - waiting for a file change is not useful in an automatic environment since there is no easy way to recover.

We have plugins that are requesting a database connection to execute stuff(TM) - if the database is offline I want my plugin to fail so the eventDaemon can reschedule event without reload shotgunEventDaemon.