Currently the only outputs plugin used is influxdb. This adds
prometheus_client outputs plugin and its directives as options.
The telegraf.conf.j2 template has been updated to check for the
outputs_prometheus_client variable and two other related variables.
New variable names and default values are shown in vars.yml.
Change-Id: I8d9380a4cc2ea58b4ad98b9fc964d45ff82090ed
Signed-off-by: Melvin Hillsman <mrhillsman@gmail.com>