We currently only run cleanup Service Hooks when a task is either
Killed, or Exited. However, due to the implementation of a task runner,
tasks are only Exited if they every correctly started running, which is
not true when you recieve an error early in the task start flow, such as
not being able to pull secrets from Vault.

This updates the service hook to also call consul deregistration
routines during a task Stop lifecycle event, to ensure that any
registered checks and services are cleared in such cases.

fixes #5770