(maint) Check for valid encoding from spawned process

When facter spawns a new process, it is possible that the encoding
for the output will come back as a non-UTF8 string; for instance,
when the locale is set to CP932 for Japanese. This can occur when
the shell injects a string into the output, such as for a command-
not-found type of error. In these cases, we should fall back to
the external default encoding, otherwise ruby will error on string
manipulations of strings that re not UTF-8.

Author: tvpartytonight

lib/facter/custom_facts/core/execution/base.rb

@@ -106,6 +106,7 @@ def execute_command(command, on_fail = nil, logger = nil, timeout = nil)
             raise Facter::Core::Execution::ExecutionFailure.new, message
           end
 
+          out.force_encoding(Encoding.default_external) unless out.valid_encoding?
           [out.strip, stderr]
         end