Ability to redirect output and return arbitrary exit codes in admin procedures

[denesterov]

There are many use-cases to use cartridge admin for some automation: gather lists of specific records or wait for some condition. e.g.

./cartridge admin -c CREDS migration_results | grep Subscriber > subs.csv

or

./cartridge admin -c CREDS get_migration_status

if [ $? -eq 0 ] 
then 
  echo "Migration finished" 
else 
  echo "Failed" 
fi