Allow to change MAIN_CLASS for entrypoint
Allow to change MAIN_CLASS for entrypoint

This allows us to configure the main class during startup.  Currently used for
running 2 containers in a kubernetes pod, where the other one is the monitor
process.

Defaults to com.pinterest.secor.main.ConsumerMain which was old behaviour

HenryCaiHaiying/secor,HenryCaiHaiying/secor,pinterest/secor,pinterest/secor