(FACT-3441) improve reliability of uname resolver

In the case that the uname command fails to return expected content,
this adds validation to the output looking for both an empty result,
or missing results.

Logging is added to help identify the condition.

lib/facter/resolvers/uname.rb

@@ -28,12 +28,16 @@ def uname_system_call(fact_name)
         def build_fact_list(output)
           uname_results = output.split("\n")
 
-          @fact_list[:machine] = uname_results[0].strip
-          @fact_list[:nodename] = uname_results[1].strip
-          @fact_list[:processor] = uname_results[2].strip
-          @fact_list[:kernelrelease] = uname_results[3].strip
-          @fact_list[:kernelname] = uname_results[4].strip
-          @fact_list[:kernelversion] = uname_results[5].strip
+          if !uname_results.empty?
+            @fact_list[:machine],
+            @fact_list[:nodename],
+            @fact_list[:processor],
+            @fact_list[:kernelrelease],
+            @fact_list[:kernelname],
+            @fact_list[:kernelversion] = uname_results.map(&:strip)
+          else
+            log.warn('Request to uname returned no output. Uname related facts are not populated.')
+          end
         end
       end
     end