GS-486: Alerts Resource

[solarchad]

Fixes #1

I was able to create/read/update/destroy the following alert resource:

resource "appoptics_alert" "myalert" {
  name        = "MyAlert"
  description = "A Test Alert"

  # services    = ["${appoptics_service.myservice.id}"]

  condition {
    type        = "above"
    threshold   = 10
    metric_name = "sawmill.go.goroutines"

    tag {
      name    = "hostname"
      grouped = true
      values  = ["12b019bd2da3"]
    }
  }
  active = true
}

[solarchad]

@trevrosen I got the tests mostly working. It looks like our hunch was correct, the tests are still failing because the alerts tests are referencing the service which uses the librato client still. So I think to resolve the tests, I'll fix up the service stuff next.

[trevrosen]

:shipit: wooooooooo! 🥂 Congrats!