* Make WorkerPools and Queues flushable

Adds Flush methods to Queues and the WorkerPool
Further abstracts the WorkerPool
Adds a final step to Flush the queues in the defer from PrintCurrentTest
Fixes an issue with Settings inheritance in queues

Signed-off-by: Andrew Thornton <art27@cantab.net>

* Change to for loop

* Add IsEmpty and begin just making the queues composed WorkerPools

* subsume workerpool into the queues and create a flushable interface

* Add manager command

* Move flushall to queue.Manager and add to testlogger

* As per @guillep2k

* as per @guillep2k

* Just make queues all implement flushable and clean up the wrapped queue flushes

* cope with no timeout

Co-authored-by: Lauris BH <lauris@nix.lv>

* Queue: Add generic graceful queues with settings

* Queue & Setting: Add worker pool implementation

* Queue: Add worker settings

* Queue: Make resizing worker pools

* Queue: Add name variable to queues

* Queue: Add monitoring

* Queue: Improve logging

* Issues: Gracefulise the issues indexer

Remove the old now unused specific queues

* Task: Move to generic queue and gracefulise

* Issues: Standardise the issues indexer queue settings

* Fix test

* Queue: Allow Redis to connect to unix

* Prevent deadlock during early shutdown of issue indexer

* Add MaxWorker settings to queues

* Merge branch 'master' into graceful-queues

* Update modules/indexer/issues/indexer.go

Co-Authored-By: guillep2k <18600385+guillep2k@users.noreply.github.com>

* Update modules/indexer/issues/indexer.go

Co-Authored-By: guillep2k <18600385+guillep2k@users.noreply.github.com>

* Update modules/queue/queue_channel.go

Co-Authored-By: guillep2k <18600385+guillep2k@users.noreply.github.com>

* Update modules/queue/queue_disk.go

* Update modules/queue/queue_disk_channel.go

Co-Authored-By: guillep2k <18600385+guillep2k@users.noreply.github.com>

* Rename queue.Description to queue.ManagedQueue as per @guillep2k

* Cancel pool workers when removed

* Remove dependency on queue from setting

* Update modules/queue/queue_redis.go

Co-Authored-By: guillep2k <18600385+guillep2k@users.noreply.github.com>

* As per @guillep2k add mutex locks on shutdown/terminate

* move unlocking out of setInternal

* Add warning if number of workers < 0

* Small changes as per @guillep2k

* No redis host specified not found

* Clean up documentation for queues

* Update docs/content/doc/advanced/config-cheat-sheet.en-us.md

* Update modules/indexer/issues/indexer_test.go

* Ensure that persistable channel queue is added to manager

* Rename QUEUE_NAME REDIS_QUEUE_NAME

* Revert "Rename QUEUE_NAME REDIS_QUEUE_NAME"

This reverts commit 1f83b4fc9b.

Co-authored-by: guillep2k <18600385+guillep2k@users.noreply.github.com>
Co-authored-by: Lauris BH <lauris@nix.lv>
Co-authored-by: techknowlogick <matti@mdranta.net>
Co-authored-by: Lunny Xiao <xiaolunwen@gmail.com>