Jopr operation returns are not shown

Generated rhq-plugin.xml does not define any returns for operations that actually return something, which means that jopr does not show output of calls like DistributionManagerImpl.locateKey()
So, two things need to happen here:
1. rhq-pluginGen needs to be enhanced to support returns (it currently does not)
2. tools/ module needs to be enhanced so that it can inspect the return of the method and populate rhq's OperationProps accordingly