No alerts for expanding a cluster

[fbalak]

I have successfully expanded a cluster but there were no notifications (email, snmp, ui) about this event as described in specification.

Reproducer:

1. Install Tendrl (via tendrl-ansible).
2. Create cluster and import it into Tendrl.
3. Add node into cluster: gluster peer probe [new_node]
4. Run tendrl-ansible with new node from the same server that installed Tendrl on all other machines.
5. Check expanded cluster and alerts.

Tested with:

tendrl-api-1.6.0-1.el7.centos.noarch
tendrl-api-httpd-1.6.0-1.el7.centos.noarch
tendrl-commons-1.6.0-1.el7.centos.noarch
tendrl-grafana-plugins-1.6.0-1.el7.centos.noarch
tendrl-grafana-selinux-1.5.4-2.el7.centos.noarch
tendrl-monitoring-integration-1.6.0-1.el7.centos.noarch
tendrl-node-agent-1.6.0-1.el7.centos.noarch
tendrl-notifier-1.6.0-1.el7.centos.noarch
tendrl-selinux-1.5.4-2.el7.centos.noarch
tendrl-ui-1.6.0-1.el7.centos.noarch

[shtripat]

@fbalak there is an event logged for the same. Will change it to notification based on how discussion goes for Tendrl/commons#849. If its user triggered (if decided later) an event is enough but if its automatic option will convert to notification.

@nthomas-redhat @r0h4n ^^^