Move #find_compiled_package to class CompileTask
Move tests for #find_compiled_package
Remove unnecessary test set-up

Signed-off-by: Jesse Zhang <jz@pivotallabs.com>
replace `block.call` with `and_yield`

Signed-off-by: Tony Hansmann <thansmann@pivotallabs.com>
privatize #compile_packages and #process_task

Signed-off-by: Tony Hansmann <thansmann@pivotallabs.com>
privatize #enqueue_unblocked_tasks