Add support for external Dynflow core

[adamruzicka]

this option is being introduced in theforeman/smart_proxy_dynflow#63

[ekohl]

Currently this is only supported on EL but would it make sense to implement this on Debian as well? Doesn't have to be the same PR, but if we have the right packages it should work and closer align the platforms.

[adamruzicka]

I'm currently looking it. I most likely won't push it into this PR, but having all the platforms unified somewhere down the road would be nice.

[iNecas]

In that case I guess we need to have the external_core set only for el-based systems.

[adamruzicka]

That makes sense. is that a thing which needs to be done here or should it go to installer/scenarios/somewhere?

[iNecas]

If possible to do this changes in a way that they would work with the old installer and it would not be too much of a hassle, I'm for doing the changes changes here (was thinking I was replying different PR.

For this question, 👍 for implementing the check here.

[iNecas]

Makes sense. The dependent changes were merged in smart_proxy_dynflow and new release has been made. Ok with with getting this in as well

[ekohl]

Just the wording in comments could be improved.