shell: better handle job output parameters
Due to openlmi's workaround of pegasus' shortcoming, JobOutParameters

property of job instance is something else then it should be. It's an

instance of __MethodParameters_<method_name>_Result class which derives

from __MethodParameters_<method_name> class. The latter contains input

parameters of asynchronous method. Therefor JobOutParameters may contain

input parameters as well. Let's filter them out because this may confuse

client scripts.