auto-restart: only wait for local jobs running on localhost

[oliver-sanders]

Cylc8 port of #3814.

Before attempting auto-restart Cylc is supposed to wait for all locally running jobs
(i.e. those submitted via background or at) on the suite host to finish.

Unfortunately this functionality is somewhat overzealous and is waiting for all jobs
submitted via background or at on any host to complete before restarting.

Some users have exceptionally long-running background jobs (pollers) which
have highlighted this bug.

Requirements check-list

• I have read CONTRIBUTING.md and added my name as a Code Contributor.
• Contains logically grouped changes (else tidy your branch by rebase).
• Does not contain off-topic changes (use other PRs for other changes).
• Already covered by existing tests.
• Appropriate change log entry included.
• No documentation update required.
• No dependency changes.

[datamel]

Approved.