Introduce a waiting process as a test utility

[cameron-craig-etas]

#588

This PR introduces a "waiting" process that goes hand-in-hand with the "counting" process being introduced in /pull/587. The process takes some required arguments to configure the semaphore name, and the expected count. Optionally, this process can be used to start from zero, which deletes the named semaphore before starting.

I've tested this locally:

• Tested that the semaphore is created and posted to correctly

$ bazel build //tests/utils/test_helper:waiting_process
$ bazel-bin/tests/utils/test_helper/waiting_process -p /namedsem
$ stat -c '%a %n' /dev/shm/sem.namedsem
644 /dev/shm/sem.namedsem
$ ./bin/python3 -c "import posix_ipc; sem = posix_ipc.Semaphore('/namedsem'); print('Value:', sem.value)"
Value: 1
$ bazel-bin/tests/utils/test_helper/counting_process  -p /namedsem
Value: 2

• Tested that errors are reported when arguments are missing

  $ bazel-bin/tests/utils/test_helper/waiting_process
  Invalid arguments! Must provide at least one option.
  
  $ bazel-bin/tests/utils/test_helper/waiting_process -n /namedsem
  Invalid arguments! An expected count must be provided.
  
  $ bazel-bin/tests/utils/test_helper/waiting_process -c
  $ bazel-bin/tests/utils/test_helper/waiting_process: option requires an argument -- 'c'
  Invalid or missing argument.
  
  $ bazel-bin/tests/utils/test_helper/waiting_process -c 10
  Invalid arguments! Must provide at least one option.
  
  $ bazel-bin/tests/utils/test_helper/waiting_process -p
  $ bazel-bin/tests/utils/test_helper/waiting_process: invalid option -- 'p'
  Invalid or missing argument.
  
  $ bazel-bin/tests/utils/test_helper/waiting_process -z
  Invalid arguments! A semaphore name must be passed if starting from zero.
  

• Tested that the process waits until the expected count is reached

  $ bazel-bin/tests/utils/test_helper/waiting_process -n /sem -c 10
  (post 10 times using counting_procees)...
  echo $?
  0
  

• Tested that the semaphore is deleted if passing -z

  $ bazel-bin/tests/utils/test_helper/counting_process -p /sem # Create sem
  $ file /dev/shm/sem.sem # Check exists
  /dev/shm/sem.sem: data
  $ bazel-bin/tests/utils/test_helper/waiting_process -z -n /sem # Delete
  $ file /dev/shm/sem.sem # Check deleted
  /dev/shm/sem.sem: cannot open `/dev/shm/sem.sem' (No such file or directory)
  

• Tested that the help option works

  $ bazel-bin/tests/utils/test_helper/waiting_process -h
  Usage: ./wait_for_semaphore --semaphore-name <semaphore_name> --expected-count <expected_count> [--timeout-seconds <timeout in seconds>] [--start-from-zero]
  $ bazel-bin/tests/utils/test_helper/waiting_process --help
  Usage: ./wait_for_semaphore --semaphore-name <semaphore_name> --expected-count <expected_count> [--timeout-seconds <timeout in seconds>] [--start-from-zero]
  

• Test that interger parsing can fail

  $ bazel-bin/tests/utils/test_helper/waiting_process -c k
  Could not parse expected-count as integer: k
  

[paulquiring]

I left some suggestions how to improve the error handling parsing the options. The suggestions do not indicate hard bugs.