Restart services when init files change?

[mattduck]

Hey, thanks for putting this together.

I just had a situation where I updated the definition for
prometheus_node_exporter_opts, but after provisioning our servers I had to
manually reload the node_exporter service to apply the changes that were made
in the init script.

I believe we could handle this automatically by adding the restart node_exporter notifier to the three tasks here:
https://github.com/William-Yeh/ansible-prometheus/blob/master/tasks/install-node-exporter.yml#L94.
Is there any reason that this would be a bad idea?

(This might also apply to the equivalent tasks for the other components).