Cache for host's fact_hash
I believe we can improve performance of cache importer by implementing a simple cache of host facts. This is used during import process to determine which facts to add/update/delete as well as in other parts of Foreman. We can simply use Rails cache and store whole hash as JSON. This will work with or without Redis or Memcache however the performance benefit will be big when using shared memory approach.
Cache invalidation will be only via fact importer and fact cleaner as there are no other means of updating facts (user cannot and should not be allowed to do this).