Fix wrong condition testing

We should try invoke method if instance has method with that name, I was
negating the condition which was wrong
New test added

Test to check success result from jsonrpc call
Typo fixes and method name change.

* Method to check json alright is assertOkJson not assertJsonOk
* use non existent method as param to jsonrpc call for testing method
  not found return value from jsonrpc

Signed-off-by: Vasudev Kamath <kamathvasudev@gmail.com>
disable python3 tests

For the time being till the modules are ported to python3 disable the
tests for py3