topgun: fix hijack_container_gc_test
topgun: fix hijack_container_gc_test

these were sensitive to there being additional image fetching containers

Signed-off-by: Alex Suraci <925ba519bbf1a06224928b692ef88b93aee946af@gmail.com>

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