New http_check recipe+template

[chrissnell]

A new recipe and template for http_check. Template uses the Ruby->JSON->YAML data structure conversion a la the JMX check recipe.

[coveralls]

Coverage remained the same at 100.0% when pulling 527372d on chrissnell:http_check into 6f29a4c on DataDog:master.

[chrissnell]

Fixed the Travis build error.

[chrissnell]

@miketheman I much prefer your new style of YAML building using the Ruby data structure. If the PR from @mtougeron is what you want to roll with, you won't hurt my feelings but we (Revinate) definitely love your new style of config and would prefer to use it.

[miketheman]

@chrissnell I'm a big fan as well - as you can see, there's a comment on that one.

I guess "whomever can get the code & tests into place first" wins? /cc: @mtougeron

[mtougeron]

ready... set... race!! haha. but in all seriousness, I'm updating PR 177 now.

[chrissnell]

You want TESTS? I think @mtougeron is going to win this one. :)

[miketheman]

Thanks for bearing with me - I rebased and reordered a touch, but we're not merged to master along with the other changesets.