tools: Adds notifier config validation prior to service startup

Executes notifier config validation prior service startup. If validation
fails, service returns error exit code.

Change-Id: I11ad77a33697f254e60e1d0b12e343900e5b0b34
Bug-Url: https://bugzilla.redhat.com/989382
Signed-off-by: Martin Perina <mperina@redhat.com>