Ensure jsonrpc threading settings are sane (#11267)

* Ensure jsonrpc threading settings are sane

Starting with `jsonrpc` v14, the "server threads" setting is more important than before and the current default of 1 means the https server is effectively single-threaded. This PR proposes a new default of 4 (and ensures that crazy settings like e.g. `0` are bumped to at least `1`).

Also included: some docs, tests and cosmetics.

* Update parity/rpc.rs

Co-Authored-By: Tomasz Drwięga <tomusdrw@users.noreply.github.com>

* Update parity/rpc.rs

Co-Authored-By: Tomasz Drwięga <tomusdrw@users.noreply.github.com>

* Remove (i.e. deprecate) `--jsonrpc-threads` command line option

* Call numbers NUM

* Don't show a default for --jsonrpc-threads (deprecated)

* Show deprecation warning when using `--jsonrpc-threads` or `processing_threads`

* Update parity/deprecated.rs

Co-Authored-By: Niklas Adolfsson <niklasadolfsson1@gmail.com>

* Fix test

* Fix tests for real
Status Job ID Name Coverage
  Test
passed #304591
linux-docker allowed to fail
cargo-audit

00:00:19

passed #304586
linux-docker
cargo-check 0 3

00:02:15

passed #304587
linux-docker
cargo-check 1 3

00:00:23

passed #304588
linux-docker
cargo-check 2 3

00:00:24

passed #304590
linux-docker
cargo-check-benches

00:02:12

passed #304589
linux-docker
cargo-check-evmbin

00:01:38

passed #304592
linux-docker
validate-chainspecs

00:01:10

 
  Build
passed #304597
linux-docker
build-android

00:20:45

passed #305080
rust-osx
build-darwin

00:18:39

passed #304598
linux-docker
build-linux

00:23:48

passed #304600
linux-docker
build-linux-arm64

00:24:57

passed #304601
linux-docker
build-linux-armhf

00:24:37

passed #304599
linux-docker
build-linux-i386

00:16:33

passed #304603
rust-windows
build-windows

00:47:31

passed #304593
linux-docker
test-cpp

00:05:24

passed #304594
linux-docker
test-linux

00:18:39

passed #304595
linux-docker
test-linux-beta

00:18:28

failed #304596
linux-docker allowed to fail
test-linux-nightly

00:08:24

failed #304602
rust-osx
build-darwin

 
  Publish
manual #304611
linux-docker allowed to fail manual
publish-av-whitelist
manual #304604
kubernetes-parity-build allowed to fail manual
publish-docker
manual #304609
linux-docker allowed to fail manual
publish-onchain-manually
manual #304610
linux-docker allowed to fail manual
publish-release-awss3-manually
manual #304607
linux-docker allowed to fail manual
publish-snap-arm64-manually
manual #304608
linux-docker allowed to fail manual
publish-snap-armhf-manually
manual #304606
linux-docker allowed to fail manual
publish-snap-i386-manually
manual #304605
linux-docker allowed to fail manual
publish-snap-manually
 
Name Stage Failure
failed
test-linux-nightly Build
    discovery::tests::removes_expired

test result: FAILED. 46 passed; 1 failed; 1 ignored; 0 measured; 0 filtered out

error: test failed, to rerun pass '-p ethcore-network-devp2p --lib'
Command exited with non-zero status 101
5632.23user 296.78system 8:08.08elapsed 1214%CPU (0avgtext+0avgdata 5014920maxresident)k
440736inputs+21534904outputs (818major+64590804minor)pagefaults 0swaps
ERROR: Job failed: exit code 1