Logstash config path need to check the permission of the file.

[ph]

The config : path option only check if the file exists, we don't check if we have the right permission to read the file, in circumstances this will lead to confusing error.

moved from logstash-plugins/logstash-input-beats#116

An unexpected error occurred! {:error=>#, :backtrace=>["/usr/share/logstash/vendor/bundle/jruby/1.9/gems/logstash-input-beats-3.1.0.beta4-java/lib/logstash/inputs/beats.rb:173:in stop'", "/usr/share/logstash/logstash-core/lib/logstash/inputs/base.rb:88:indo_stop'", "org/jruby/RubyArray.java:1613:in each'", "/usr/share/logstash/logstash-core/lib/logstash/pipeline.rb:366:inshutdown'", "/usr/share/logstash/logstash-core/lib/logstash/agent.rb:252:in stop_pipeline'", "/usr/share/logstash/logstash-core/lib/logstash/agent.rb:261:inshutdown_pipelines'", "org/jruby/RubyHash.java:1342:in each'", "/usr/share/logstash/logstash-core/lib/logstash/agent.rb:261:inshutdown_pipelines'", "/usr/share/logstash/logstash-core/lib/logstash/agent.rb:123:in shutdown'", "/usr/share/logstash/logstash-core/lib/logstash/runner.rb:237:inexecute'", "/usr/share/logstash/vendor/bundle/jruby/1.9/gems/clamp-0.6.5/lib/clamp/command.rb:67:in run'", "/usr/share/logstash/logstash-core/lib/logstash/runner.rb:157:inrun'", "/usr/share/logstash/vendor/bundle/jruby/1.9/gems/clamp-0.6.5/lib/clamp/command.rb:132:in run'", "/usr/share/logstash/lib/bootstrap/environment.rb:66:in(root)'"], :level=>:fatal}

[purbon]

This might be easy to extend and control if something like #5778 get's in.