Don't reconnect st2 DB/MQ on failure, exit early instead

[warrenvw]

Moved from https://github.com/StackStorm/st2enterprise-dockerfiles/issues/57

The current/default StackStorm tries to reconnect to Mongo or RabbitMQ on failure.
This is undesired behavior in K8s environment where engine handles failover by rescheduling exited process.
So the desired configuration is to exit fast any st2 service on failure without reconnection and let K8s handle it.

Luckily, these settings are configurable in st2.conf:
https://github.com/StackStorm/st2/blob/master/conf/st2.conf.sample#L179
https://github.com/StackStorm/st2/blob/master/conf/st2.conf.sample#L109

Hardcode them in default st2.conf (during the Docker image build) to not reconnect, but exit st2 on failure.