Simplify partial map Py3 IDL test added by commit a59912a0

Simplify partial map Py3 IDL test added by commit a59912a0

Commit a59912a0 ("python: Add support for partial map
and partial set updates") added unit tests for the partial
map function for the python IDL.  However, because Python3
doesn't order dictionaries consistently, this
test is a crap shoot for systems that support Python3.

As a short term fix, do not use a dictionary with multiple
elements for the partial map test case.

Change-Id: Ibdec10ebd895051321b9bff7d9fe8a7e0bd9eb88
Signed-off-by: Ryan Moats <rmoats@us.ibm.com>
Signed-off-by: Ben Pfaff <blp@ovn.org>