Test Scenario: fix support for default stateless kieSession

How to reproduce:

• edit kmodule.xml and create only a default stateless session

  <kmodule xmlns="http://www.drools.org/xsd/kmodule" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
    <kbase name="myKieBase">
      <ksession name="mySession" type="stateless" default="true"/>
    </kbase>
  </kmodule>
  

• create a Rule test scenario and specify in Setting panel stateless
• run

Without the fix:
Test failed with this exception "Impossible to find a KieSession with name null"

With the fix:
The test should be able to run because that kmodule configuration is valid