tests for integration classes

[kitchen]

these are tests for the integration classes.

I have left out 2 integrations:

1. datadog_agent::integration::directory

   This integration doesn't appear to be functional. Catalogs which include it cannot compile. I've opened an issue at datadog_agent::integrations::directory is not functional? #144 for this.

2. datadog_agent::integration::generic

   The work I plan to do next on this will obviate the need for the 'generic' integration, so it didn't make sense adding tests for something that's going to go away Real Soon Now™

[kitchen]

I made each test into a separate commit for easier perusal of the changes related to that test. I can squash this before merging if necessary.

[talwai]

@kitchen looks great, thanks for your efforts! We'll be reviewing this more thoroughly shortly, and have it slated for an upcoming release

[irabinovitch]

@truthbk Will we be able to pull these test improvements into 1.7.0 as well? (#176)

[truthbk]

Yup, put these into #176, some had to be slightly modified due to changes that were brought in other PR's, but these are great! Thanks a lot @kitchen, big boost for us in the spec coverage. Much appreciated.

[truthbk]

@kitchen just wanted to let you know there was a typo in the changelog that shipped with the released puppet module 1.7.0 that failed to recognize your contribution, it's already been fixed in github and will be corrected in subsequent releases. My apologies for the oversight, your changes were the last I added andI forgot to update before releasing 😞