EXpandFlags: preinstallexpand vs 'aggregate' - aggregate not possible if dep chains for vminstall/preinstall not satisfied

[DimStar77]

Issue Description

Since the introduction of ExpandFlags: preinstallexpand in openSUSE Factory, every now and then we can run into a weird 'trouble case'

Say, by error, we remove a package that was needed by RPM (let's assume lua54) - without preinstallexpand, we could 'simply aggregate binaries from a known good place into openSUSE:Factory (usually we'd do lua54-AGGR) and have OBS rebuild 'lua54' based on the aggregated binaries.

With preinstallexpand, this does not work, as OBS 'fails to calculate the setup' - even though a VM Setup is not needed to aggregate existing binaries.

Expected Result

Package aggregates should be doable even when expandflags is defined and dep chains to build VMs would be broken

How to Reproduce

• wipe binaries of any package one of the Preinstall packages depends on
• => the dep chain is broken, as expected; no builds can start
• Try to recover by aggregating known good binaries
  => The aggregate can also not start, as the project setup claims to be broken.