[test][worker] Get random port rather than using a fixed number

This will allow to run several tests in parallel.
7 jobs for fix_worker_tests in 57 minutes and 28 seconds (queued for 9 seconds)
Status Name Job ID Coverage
  Build
passed build_linux_27 #138655
docker

00:06:09

60.0%
passed build_linux_36 #138656
docker

00:05:45

60.0%
passed build_macosx_27 #138657
macosx

00:08:29

60.0%
passed build_macosx_36 #138658
macosx

00:08:16

60.0%
 
  Docker
passed docker_linux_27 #138666
docker-build

00:21:45

70.0%
passed docker_linux_36 #138660
docker-build

00:27:13

70.0%
failed docker_linux_27 #138659
docker-build

00:26:51

70.0%