Added the tests for the new methods (get_default_config_xml and set_config_xml) of the BigBlueButton 0.81. Refs #1129
Add more tests for the changes made for BBB 0.81

The only missing tests now are for BigBlueButton::BigBlueButtonConfigXml.

refs #1129
Add the last missing tests for the changes made for BBB 0.81

refs #1129