atc: test args used when calling RunCheckStep
atc: test args used when calling RunCheckStep

the previous set of tests were mostly focused on the failure branches,
lacking verifying that we're creating the structs with what we expect,
and actually using them when calling RunCheckStep.

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

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