This is just a very minor directory organization change, but it has the
advantage of keeping a bunch of files out of the root directory and
packaging them together since they are related to each other.
Now, our `integration_tests/` directory has a nice pattern of
setup/cleanup/test.sh scripts at the top global level and at each module
level:
```
❯ tree --dirsfirst integration_tests
integration_tests
├── mysql
│ ├── util
│ │ ├── launch_mysql_container.sh
│ │ └── wait_for_mysqld.sh
│ ├── cleanup.sh
│ ├── setup.sh
│ ├── single_run.sh
│ └── test.sh
├── ssh
│ ├── cleanup.sh
│ ├── setup.sh
│ └── test.sh
├── cleanup.sh
├── setup.sh
└── test.sh
3 directories, 12 files
```
The scripts are runnable via:
```
./integration_tests/setup.sh && ./integration_tests/test.sh && ./integration_tests/cleanup.sh
```
