containerd: backfill tests
containerd: backfill tests

The behaviour of the Destroy function was changed and therefore tests had to be
rewritten.

Co-authored-by: Ciro Costa <4f5054ab2db051d03adf9068233a850c82b24437@pivotal.io>
Signed-off-by: Ciro S. Costa <4f5054ab2db051d03adf9068233a850c82b24437@pivotal.io>

concourse/concourse,concourse/concourse,concourse/concourse,concourse/concourse,concourse/concourse