fix concurrent test-server errors

[SourceR85]

Motivation

GitHub Actions recycling test container, causing workflows "First retry" and "Second retry" to fail, because the express-server port is already in use.

Error

> npm run build-test && node ./bin/test-browser.js

events.js:377
      throw er; // Unhandled 'error' event
      ^

Error: listen EADDRINUSE: address already in use :::3000
    at Server.setupListenHandle [as _listen2] (net.js:1331:16)
    at listenInCluster (net.js:1379:12)
    at Server.listen (net.js:1465:7)
    at Function.listen (/home/runner/work/pouchdb/pouchdb/node_modules/express/lib/application.js:618:24)
    at Object.<anonymous> (/home/runner/work/pouchdb/pouchdb/tests/misc/pouchdb-express-router.js:31:5)
    at Module._compile (internal/modules/cjs/loader.js:1114:14)
    at Object.Module._extensions..js (internal/modules/cjs/loader.js:1143:10)
    at Module.load (internal/modules/cjs/loader.js:979:32)
    at Function.Module._load (internal/modules/cjs/loader.js:819:12)
    at Function.executeUserEntryPoint [as runMain] (internal/modules/run_main.js:75:12)
Emitted 'error' event on Server instance at:
    at emitErrorNT (net.js:1358:8)
    at processTicksAndRejections (internal/process/task_queues.js:82:21) {
  code: 'EADDRINUSE',
  errno: -98,
  syscall: 'listen',
  address: '::',
  port: 3000
}

Shadows another error

Run npm test
  npm test
  shell: /usr/bin/bash -e {0}
  env:
    NODE_VERSION: 14
    SELENIUM_HUB_HOST: hub
    TEST_HOST: localhost
    CLIENT: node
    SERVER: pouchdb-server
mkdir: cannot create directory ‘pouchdb-server-install’: File exists

npm ERR! Test failed.  See above for more details.
> pouchdb-monorepo@7.0.0-prerelease test /home/runner/work/pouchdb/pouchdb
> ./bin/run-test.sh

Error: Process completed with exit code 1.

Solution

1. run-test.sh tests the port before starting pouchdb-express-router,
   if the port isn't free, it simply increments the port.
2. skip down-server instantiation, if port 3010 isn't free.
3. skip pouchdb-server-install build & run, if the directory exists

With this patch, GitHub-CI should only fail on if one of the test cases fail.

[SourceR85]

I think, I've got it now.

With this patch, GitHub-CI should only fail on if one of the test cases fail.

(side note: test-handling should be improved, but that's a story for another PR)

[garethbowen]

Looks good to me. Thanks!