fix responseXml mess in acceptance test code

[individual-it]

in BasicStructure.php we have getResponseXml that returns an the content of the response parsed into a SimpleXMLElement
in WebDav.php we have $this->responseXml what is an array and $this->responseXmlObject that is a SimpleXMLElement. getResponseXmlObject() returns the SimpleXMLElement and no getter for responseXml (Array)

this is all a bit confusing and need refactoring

[ownclouders]

GitMate.io thinks the contributor most likely able to help you is @phil-davis.

Possibly related issues are #22492 (test), #22485 (test), #31579 (test), #32378 (Small fixes in acceptance tests), and #34292 (progress of automated acceptance tests for locks).