subscription_type check is performed against symbol

```
./oo-install-ose -c oo-install-cfg.yml -e -s rhn -u $u -p $p -w enterprise_deploy
```
will fail with _Subscription type 'rhn' is not recognized_ because _case_ check is performed against :symbol in oo-install/lib/installer/subscription.rb:subscription_info but string is passed as argument.