* tests: Update testing submodules (bats-assert, bats-support)
These two submodules were migrated to the `bats-core` organization, where they continued to receive updates.
* tests: Use tagged release of `bats-core/bats-support`
This is technically one commit backwards, but no relevant difference has been made since, other than moving the submodule to the `bats-core` organization.
* tests: Bump `bats-assert` to August 2022 (master)
No official release tag since Nov 2018, but a fair amount of changes since then.
* tests: Bump `bats-core` to `v1.7.0` release
* tests(fix): Correctly use assertions
Some tests were updated as the upgrade of bats submodules had `assert` methods raise awareness of incorrect usage.
This additionally revealed some existing tests that weren't meant to be using `run`, which swallowed failures from surfacing.
* Added `bats-assert` for more detailed error, very useful locally and on Travis
* Moved `bats` to git submodule
Example:
```
not ok 52 checking opendkim: generator creates keys, tables and TrustedHosts
# (from function `assert_output' in file test/test_helper/bats-assert/src/assert.bash, line 239,
# in test file test/tests.bats, line 368)
# `assert_output 2' failed
#
# -- output differs --
# expected : 2
# actual : 4
# --
#
```
