Changed format of metrics published to Kafka as a JSON

[IzabellaRaulin]

Summary of changes:

• added formatting "the metrics to publish" based on incoming metrics types
• adjusted integration tests

Before:

Before the published data looks like below:

[{"namespace":[{"Value":"intel","Description":"","Name":""},{"Value":"mock","Description":"","Name":""},{"Value":"foo","Description":"","Name":""}],"last_advertised_time":"0001-01-01T01:22:00.597278575+01:22","version":0,"config":{"name":"bob","password":"secret","user":"root"},"data": 68,"tags":{"plugin_running_on":"devmachine"},"Unit_":"","description":"","timestamp":"2016-07-20T14:00:34.597278575+02:00"}]

Notice that namespace is represented by core.Namespace struct and could be illegible to publish it in that form.

After changes:

• publish namespace as a single string
• do not publish config items (can contain passwd and so on; moreover, tags should be used to expose an additional information)
• do not publish metric's description (overhead)
• changed the order of published metric's fields

[{"timestamp":"2016-07-22T13:58:33.193748361+02:00","namespace":"/intel/mock/foo","data":68,"unit":"","tags":{"plugin_running_on":"devmachine"},"version":0,"last_advertised_time":"2016-07-22T13:58:28.68173158+02:00"}]

FYI, To consume the data from Kafka the following command was used:

docker run --rm ches/kafka kafka-console-consumer.sh --topic snap --from-beginning 
> --zookeeper <zookeeper_ip>:2181 > kafka_output.json

Tests done:

• unit tests
• integration tests

@intelsdi-x/plugin-maintainers

[andrzej-k]

@IzabellaRaulin Does this change requires documentation and unit tests update?

[IzabellaRaulin]

Thanks @andrzej-k for review. I added in README.md section presenting the format of published data + test which covers func formatMetricTypes().

[andrzej-k]

Nicely done @IzabellaRaulin 👍