added fix for python test client

added fix for the test file and added the __init__.py file that caused the module not to be installed correctly.


With catkin python exports should structured in modules.
This means that the import statement slightly changes( as shown in test_json_prolog)
for knowrob this only effects this file and two files from knowrob_addons(https://github.com/knowrob/knowrob_addons/pull/16)...


btw the line  

import roslib; roslib.load_manifest('json_prolog')

is not needed any more!