This change adds the ability to set the fields `success_before_passing` and
`failures_before_critical` on Consul service check definitions. This is a
feature added to Consul v1.7.0 and later.
  https://www.consul.io/docs/agent/checks#success-failures-before-passing-critical

Nomad doesn't do much besides pass the fields through to Consul.

Fixes #6913