Customize the DNS service (fixes #545)

[slauger]

This PR adds some options to enable the customization the DNS service. See #545 for more information.

[hashicorp-cla]

All committers have signed the CLA.

[kschoche]

Hi @slauger thanks for submitting this PR, it looks good so far, just a couple comments :
When we introduce new fields in values/templates we try to create coverage in the bats test to be sure there are no regressions, and validate the new fields work as intended.

Could you add a new test to cover these changes in test/unit/dns-service.bats ?

You can run this via bats test/unit/dns-service.bats

Also it is currently failing the following bats test:
✗ dns/Service: specified clusterIP (in test file test/unit/dns-service.bats, line 84)

Thanks!

[lkysow]

Oops! Sorry I didn't see @kschoche's comment.

Thanks for the PR! Can you add tests for these two settings (see https://github.com/hashicorp/consul-helm/blob/master/CONTRIBUTING.md#writing-unit-tests).

[slauger]

Hi,

sorry, for the late response. I'm already familiar with the usage of bats and CircleCI. Tests are added. Let me know what you think.

I also introduced dns.additionalSpec, just as ui.additionalSpec. This also obsoletes dns.clusterIP, but i would keep the parameter for backwards compatibility.

[lkysow]

This looks great!