Updates to NoTask to prevent argparse error

[ghackebeil]

This issue will track changes related to the thread here: https://groups.google.com/forum/#!topic/pyomo-forum/Att_92wrAoI

It looks like the attempt to create an argument parser by the global NoTask object in pyutilib.workflow.task is preventing a user from executing a Pyomo script from C code. I don't know whether or not this is highlighting a problem within the argparse module, but a reasonable change on our part would be to just not create an argument parser for the NoTask object (I can't see how it would be needed).