Simplify and make TOML config rendering more flexible

[rremizov]

I was trying to configure SNMP plugin and discovered that the current Role Vars schema doesn't support the following part:

  [[inputs.snmp.field]]
    oid = "RFC1213-MIB::sysUpTime.0"
    name = "uptime"

  [[inputs.snmp.field]]
    oid = "RFC1213-MIB::sysName.0"
    name = "source"

So, instead of using the template syntax to render a correct toml config we use here a custom filter which converts yaml to toml. Such an approach considerably simplifies the template and allows to create complex configurations. There are some minor downsides though:

1. The custom filter requires toml module installed on the machine running Ansible.
2. I had to bump the min_ansible_version to 2.0.

@rossmcdonald What do you think?

[rossmcdonald]

@rremizov I like this change a lot, as the current configuration templating was always a mess to maintain. I don't think requiring the toml package or Ansible v2 are problematic. Let me play around with this for a few days to test the behavior.