Run SCAPtimony's db operations before foreman_openscap's

There will be dependencies on SCAPtimony later on.
Introduce AuditableHost

as a link between Foreman's Host and SCAPtimony's Asset.
Initialize host--asset mapping by HostExtension.
Connection should be defined with inverse_of.
Connect SCAPtimony's asset with Foreman's host when uploading ARF.