Graceful shutdown for the task manager (#6654)

* Initial commit

Forked at: 74655ede


Parent branch: origin/master

* Move task_manager.rs to mod.rs

* Graceful shutdown for the task manager

* Await all background task JoinHandle at the same time

* Add tests

* Make future() wait also for exit signal + fix essential task failed

Probably related to https://github.com/paritytech/cumulus/issues/111

* add comments for non-obvious code

* Use clean_shutdown() in sc-cli

* Adapt code and upgrade tokio in sc-cli

* cleanup spacing in doc

* Add license

* I guess actually running the clean shutdown would be a good idea

* fix tests

* Update client/cli/src/runner.rs

Co-authored-by: Benjamin Kampmann <ben@gnunicorn.org>

* Improve error logging

* disable other tests (can't reproduce on my machine)

* Revert "disable other tests (can't reproduce on my machine)"

This reverts commit c133c590f33c253123ba0555ce719a71ededd60d.

* It is possible that the tasks are ended first

* Revert "It is possible that the tasks are ended first"

This reverts commit 502aba4a49fb5d892e704c412b8a81768a3f2c71.

* Use single threaded scheduler for more predictability

* enable_time

* Revert "enable_time"

This reverts commit 4e152140764a4bddeedff06a4e36ec701909e8c7.

* Revert "Use single threaded scheduler for more predictability"

This reverts commit ee5e13c5f13ff71e012dcda13579dffeb15f8ffc.

* Revert "Revert "It is possible that the tasks are ended first""

This reverts commit 1b91a8ca3eebbdc18be199c8ca188e88669ae649.

* This cannot be verified either with a threaded pool

* Apply suggestions from code review

Co-authored-by: Bastian Köcher <bkchr@users.noreply.github.com>

Co-authored-by: Benjamin Kampmann <ben@parity.io>
Co-authored-by: Benjamin Kampmann <ben@gnunicorn.org>
Co-authored-by: Bastian Köcher <bkchr@users.noreply.github.com>