A recent refactor replaced `create_or_find_by` with `create` in RhsmFactParser#operatingsystem, re-introducing a race condition that had previously been fixed. Under concurrent bulk registration, multiple hosts try to create the same OS record simultaneously, causing PG::UniqueViolation on index_operatingsystems_on_title.

Fix: restore `create_or_find_by` (atomic insert with conflict fallback) and use `find_by_attributes` (the multi-constraint lookup introduced by the same refactor) as the last-resort fallback — combining the best of both fixes.