roles/common: Use systemd module instead of "service"

This was new in Ansible 2.2 but I didn't notice until now. All of our
servers are running distributions with systemd so let's just use this.

roles/common/handlers/main.yml

@@ -8,10 +8,10 @@
   service: name=iptables-persistent state=restarted
 
 - name: reload sshd
-  service: name={{ sshd_service_name }} state=reloaded
+  systemd: name={{ sshd_service_name }} state=reloaded
 
 - name: reload sysctl
   command: sysctl -p /etc/sysctl.conf
 
 - name: restart firewalld
-  service: name=firewalld state=restarted
+  systemd: name=firewalld state=restarted