Integration tests: container cleanup in applier subpackage
Integration tests: container cleanup in applier subpackage

The integration testing suite for the applier subpackage creates two
containers for each test image, since this is necessary for testing sharding
functionality. Upon test completion, both containers are stopped but were not
destroyed. However, since all other package/subpackage testing suites only use
a single container per image, leaving the second container around is often
unnecessary.

This commit changes the applier subpackage's testing suite to only keep the
first container (per image) around, while destroying the second container.

skeema/skeema