CompileTask always receives initial_job

Avoid speculative generality that was making this code harder to reason about

Signed-off-by: Abhijit Hiremagalur <abhi@pivotallabs.com>
ReleaseVersion can determine package dependencies

[#55022292]

Signed-off-by: Rob Day-Reynolds <rdayreynolds@pivotallabs.com>
Rename DeploymentPlan::Release to ReleaseVersion

Old name was misleading since it corresponds to a ReleaseVersion not a Release

[#55022292]

Signed-off-by: Rob Day-Reynolds <rdayreynolds@pivotallabs.com>