(maint) Improve freebsd-version failure management

This program is always supposed to be found and return the expected
output on FreeBSD but make sure it runs successfully, catpure stderr in
case it becomes used at some point, and do not raise exceptions if the
resolver fails.

lib/facts/freebsd/os/release.rb

@@ -10,6 +10,8 @@ class Release
         def call_the_resolver
           installed_userland = Facter::Resolvers::Freebsd::FreebsdVersion.resolve(:installed_userland)
 
+          return [] if installed_userland.nil?
+
           value = build_release_hash_from_version(installed_userland)
 
           [Facter::ResolvedFact.new(FACT_NAME, value),

lib/resolvers/freebsd/freebsd_version_resolver.rb

@@ -15,11 +15,14 @@ def post_resolve(fact_name)
           end
 
           def freebsd_version_system_call(fact_name)
-            output, _status = Open3.capture2('/bin/freebsd-version -kru')
+            output, _stderr, status = Open3.capture3('/bin/freebsd-version -kru')
+            return nil unless status.success?
 
             build_fact_list(output)
 
             @fact_list[fact_name]
+          rescue Errno::ENOENT
+            nil
           end
 
           def build_fact_list(output)

spec/facter/resolvers/freebsd/freebsd_version_resolver_spec.rb

@@ -2,11 +2,13 @@
 
 describe Facter::Resolvers::Freebsd::FreebsdVersion do
   before do
-    allow(Open3).to receive(:capture2)
+    status = double('status')
+    allow(status).to receive(:success?).and_return(true)
+    allow(Open3).to receive(:capture3)
       .with('/bin/freebsd-version -kru')
-      .and_return('13.0-CURRENT
+      .and_return(['13.0-CURRENT
         12.1-RELEASE-p3
-        12.0-STABLE')
+        12.0-STABLE', nil, status])
   end
 
   it 'returns installed kernel' do