Replace confusing member name

Replace the member name 'data' in test_object_slo.py and
test_object_temp_url_negative.py with 'content', because 'data' member
is used as a class member name for the instace of DataGenerator in the parent
BaseObjectTest class.

Change-Id: I24f102531afaffd7e797e588777d4621be7a1084
Closes-bug: #1276835
Merge "Replace confusing member name"