jsonutils.load() accepts file pointer, not string

Renamed jsonutils.load() argument name to more appropriate one. This
name is also used in stdlib json documentation [1].

1: https://docs.python.org/2/library/json.html#json.load

Change-Id: Ia0cfce0e023ce29d3aad80a71039343643820bb4
(cherry picked from commit 9e5a39389c866d3e0901edc618e7cd364a49dbce)