e2e: add test for restarts and rescheduling remote tasks

As discussed in https://github.com/hashicorp/nomad/pull/10248#discussion_r622172830 Remote Task Drivers lack E2E testing for restarts and rescheduling.

Rescheduling in particular is interesting for remote task drivers as we have the choice of either detaching from the remote task and hoping the new placement can recover it -- or stopping the remote task and letting the replacement node start up a new one.

The latter (stopping the remote task) is less likely to leak remote tasks, so should be considered the default path.

Start by reading the discussion in PR #10248, especially the referenced review thread, then locate the existing E2E coverage for remote task drivers. Add coverage for task restarts and rescheduling, including the choice between detaching and stopping the remote task; done means the tests verify the intended behavior and prevent leaked remote tasks.

Written by the indexing model from the issue text.