Exits mon-evaluator process when encountered by a database exception

Database errors could mean database node failure. In this cases, the process
should exit so it could be automatically restarted (when handled by Docker Swarm, K8s, etc)
so it can obtain a new DB connection to an alive node.

Change-Id: I2575062d4bd23b3902b7c2ed14553d5201933002
Signed-off-by: Benjamin Diaz <bdiaz@whitestack.com>