Install isc-dhcp-server after rendering configs

[iljarotar]

Closes #357

[robertvolkmann]

Do you understand why we don't notify a handler to restart isc-dhcp-server when its configuration is changed?

tasks:
- name: render dhcpd conf
  template:
    src: dhcpd.conf.j2
    dest: /etc/dhcp/dhcpd.conf
  notify: Restart isc-dhcp-server
  - …

handlers:
  - name: Restart isc-dhcp-server
    service:
      name: "{{ dhcp_service_name }}"
      state: restarted

I also miss a daemon-reload: true.