console output: check stdout being available

[urso]

Check stdout being available when init the console output. Return error and quit beat if check fails.

[andrewkroh]

From urso: https://play.golang.org/p/OOiCvQuYB1

[inqueue]

The error looks like this when beats is running as a service where there is no stdout:

Jul 14 14:51:02 grok /usr/bin/filebeat[22191]: log.go:113: Harvester started for file: /var/log/nginx/error.log
Jul 14 14:51:04 grok /usr/bin/filebeat[22191]: output.go:92: Error bulk publishing events: write /dev/stdout: invalid argument