* fix: Workaround `postconf` write settle logic
After updating `main.cf`, to avoid an enforced delay from reading the config by postfix tools, we can ensure the modified time is at least 2 seconds in the past as a workaround. This should be ok with our usage AFAIK.
Shaves off 2+ seconds roughly off each container startup, reduces roughly 2+ minutes off tests.
* chore: Only modify `mtime` if less than 2 seconds ago
- Slight improvement by avoiding unnecessary writes with a conditional check on the util method.
- Can more comfortably call this during `postfix reload` in the change detection cycle now.
- Identified other tests that'd benefit from this, created a helper method to call instead of copy/paste.
- The `setup email restrict` command also did a modification and reload. Added util method here too.
* tests(fix): `mail_smtponly.bats` should wait for Postfix
- `postfix reload` fails if the service is not ready yet.
- `service postfix reload` and `/etc/init.d/postfix reload` presumably wait until it is ready? (as these work regardless)
* chore: Review feedback - Move reload method into utilities
Allows for using `load` with an absolute path instead of a relative one, which makes it possible to group tests into different directories.
Parallel tests differ slightly, loading the newer `helper/common.bash` and `helper/setup.bash` files instead of the older `test_helper/common.bash` which serial tests continue to use.
- `test_helper.bats` needs more work than this PR provides to be compatible with parallel tests, so must remain as a serial test for now.
- `spam_bounced.bats` had failures as a serial test, but works well converted to a parallel test in a future commit.
