tests: Adjust parallel tests

- The usual serial to parallel test conversion to utilize the `setup.bash` common setup structure, and adding a `TEST_PREFIX` var for each test case to leverage.
- Standardize on parallel test naming conventions for variables / values.
- More consistent use of `bash -c` instead of `/bin/bash -c` or `/bin/sh -c`.
- Using the `_run_in_container` helper instead of `run docker exec ${CONTAINER_NAME}`.
- Updates tests to use the `check_if_process_is_running` helper.

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chore: Revise inline docs for the `ssl_letsencrypt` test

- Moves the override to be in closer proximity to the `initial_setup` call, and better communicates the intent to override.
- Removes top comment block that is no longer providing value or correct information to maintainers.
- Revised `acme.json` test case inline doc comments.

test/helper/common.bash

@@ -30,10 +30,10 @@ function _default_teardown() {
 
 # @param ${1} program name [REQUIRED]
 # @param ${2} container name [IF UNSET: ${CONTAINER_NAME}]
-function _check_if_process_is_running() {
+function check_if_process_is_running() {
   local PROGRAM_NAME=${1:?Program name must be provided explicitly}
   local CONTAINER_NAME=${2:-${CONTAINER_NAME}}
-  _run_in_container_explicit "${CONTAINER_NAME}" pgrep "${PROGRAM_NAME}"
+  docker exec "${CONTAINER_NAME}" pgrep "${PROGRAM_NAME}"
 }
 
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