Preserve task tags when registering with discovery info

[dylanmei]

Tags have been getting lost when registering tasks that also include discovery info.

Before-and-after example

• Framework: ElasticSearch
• Executor: a Task named "elasticsearch" with a Mesos label tags=test

Before the change (with some fields omitted)

$ curl -s consul:8500/v1/catalog/service/elasticsearch | jq .
[{
    "Node": "mesos-follower-1",
    "ServiceName": "elasticsearch",
    "ServiceTags": [
      "CLIENT_PORT"
    ],
    "ServicePort": 9200
  }, {
    "Node": "mesos-follower-1",
    "ServiceName": "elasticsearch",
    "ServiceTags": [
      "TRANSPORT_PORT"
    ],
    "ServicePort": 9300
}]

After the change, notice test is included in ServiceTags.

$ curl -s consul:8500/v1/catalog/service/elasticsearch | jq .
[{
    "Node": "mesos-follower-1",
    "ServiceName": "elasticsearch",
    "ServiceTags": [
      "test",
      "CLIENT_PORT"
    ],
    "ServicePort": 9200
  }, {
    "Node": "mesos-follower-1",
    "ServiceName": "elasticsearch",
    "ServiceTags": [
      "test",
      "TRANSPORT_PORT"
    ],
    "ServicePort": 9300
}]

[ChrisAubuchon]

Looks good. Thanks!

[dylanmei]

Awesome. Cheers!