fix regression: printing default config file path

[urso]

Resolves: #2058

sample output:

Usage of ./filebeat:
  -E value
        Configuration overwrite (default null)
  -N    Disable actual publishing for testing
  -c path
        Configuration file path (default /Users/urso/.gvm/pkgsets/go1.6/global/src/github.com/elastic/beats/filebeat/filebeat.yml)
  -configtest
        Test configuration and exit.
  -cpuprofile string
        Write cpu profile to file
  -d string
        Enable certain debug selectors
  -e    Log to stderr and disable syslog/file output
  -httpprof string
        Start pprof http server
  -memprofile string
        Write memory profile to this file
  -path.config string
        Configuration path
  -path.data string
        Data path
  -path.home string
        Home path
  -path.logs string
        Logs path
  -v    Log at INFO level
  -version
        Print the version and exit