FEATURE: Allow setting Filebeat Docker filesystem and Docker binds via pillar

[weslambert]

Similar to how we are doing this for Logstash, we should allow for custom Docker binds for Filebeat.

Ex:

In pillar:

filebeat:
  docker_options:
    filesystem_bindings:
      - /myfile1onhost:/myfile1incontainer:ro
      - /myfile2onhost:/myfile2incontainer:ro

In init.sls:

{% set DOCKER_OPTIONS = salt['pillar.get']('filebeat:docker_options', {}) %}

{% for BINDING in DOCKER_OPTIONS.filesystem_bindings %}
      - {{ BINDING }}
{% endfor %}

[TOoSmOotH]

This was added in 2.4 for all containers that need these options.