Duplicate kwargs in bash_app call rather than modifying reusable dict

[benclifford]

The xfailing test for this needed updating a bit to reflect
recent changes in parsl.

Fixes issue #1058

[yadudoc]

This still wouldn't save us if the kwargs include say another dict, or list.
I'm not sure if it's worth making a deep copy every time either.

[benclifford]

What goes wrong in the case that the default value is a dict? It can be modified by an app running in a local thread executor and I think that modification is seen by all invocations, which is correct python semantics. In the case of a different-process executor like HTEX those modifications don't change the submit side values, which is parsl's behaviour for any objects passed in as a parameter.

[yadudoc]

I tested this out a bit, and i don't think the situation where one of the args is a dict itself, is a concern for us.