Avoid exceptions for zone facts on FreeBSD

FreeBSD currently loads all Solaris facts, but FreeBSD does not have
"zones", and the zone related facts fail hardly when being processed.

Improve error detection when building the zone facts, and do not emit
these facts when an error occurred.

Author: smortex

lib/facts/solaris/solaris_zones/zone.rb

@@ -21,6 +21,8 @@ def call_the_resolver
           zones = {}
 
           results = Facter::Resolvers::SolarisZone.resolve(:zone)
+          return unless results
+
           results&.each do |result|
             zones.merge!(parse_result(result))
             resolved_facts << create_legacy_zone_facts(result)

lib/resolvers/solaris/solaris_zone_name.rb

@@ -14,6 +14,8 @@ def post_resolve(fact_name)
         end
 
         def build_current_zone_name_fact(fact_name)
+          return unless File.executable?('/bin/zonename')
+
           zone_name_output, status = Open3.capture2('/bin/zonename')
           unless status.to_s.include?('exit 0')
             @log.debug("Command #{command} returned status: #{status}")

lib/resolvers/solaris/zone_resolver.rb

@@ -14,6 +14,8 @@ def post_resolve(fact_name)
         end
 
         def build_zone_fact(fact_name)
+          return unless File.executable?('/usr/sbin/zoneadm')
+
           command = '/usr/sbin/zoneadm list -cp'
           zone_adm_output, status = Open3.capture2(command)
           unless status.to_s.include?('exit 0')