wrapper: use output option as the destination to output by not running groonga

Example (output by not running groonga): groonga --help
Use non duplicated name

pretty_print ->
use_pretty_print

pretty_print is the method in PP class used assetions.
wrapper: don't exit in #run

Wrapper#run is called by bin/grnline, so it should return a value.
wrapper: return the exit status to the executable file by Wrapper#run