Fix hypervisor without any guest

As by RedHatSatellite#68, if a host does not have any guest, and facts is not populated, fail.
The resolution is to make use of virtwho option, which will gather the facts from virtwho directly.
Still no fatal error will be given anymore after the patch, but a WARNING in stderr.
This is due to a candlepin bug which does not expose (yet) the facts for a hypervisor.

katello-attach-subscription

@@ -849,6 +849,9 @@ def vdcupdate()
     system_details[system['name']]=sys
     # check if the type requested match the host one
     system_type = KatelloAttachSubscription::FactAnalyzer.system_type(sys)
+    if system_type == KatelloAttachSubscription::FactAnalyzer::HYPERVISOR
+      STDERR.puts "  WARNING: host #{system['name']}' id #{system['id']} has not been recognized. This may happens because of a HYPERVISOR does not have any guest. Try to leverage on virtwho option."
+    end
     # for each item in yaml extract sub
     if @options[:debug]
       puts " DEBUG: YAML dump with all definitions for the current system"

lib/katello_attach_subscription/fact_analyzer.rb

@@ -36,6 +36,10 @@ def self.system_type_from_host(host)
 
     def self.system_type(host, facts = nil)
       facts = host['facts'] unless facts
+      # workaround, if a host does not have a valid list of facts, the code will fail in self.system_type_from_facts(facts)
+      if not facts.is_a?(Hash)
+        facts = {}
+      end
       self.system_type_from_host(host) || self.system_type_from_facts(facts) || UNKNOWN
     end
   end