Fix test code so it can run cleanly on servers not supporting mkcalendars

[tobixen]

According to the RFC, it's perfectly allowed for a caldav server to deny creating new calendars. Also, even if it should be possible to make new calendars, we've seen problems with it on some servers. Currently pretty much all the functional tests starts by creating a new test calendar. We need to make support in the test framework for running as many tests as possible towards the default calendar rather than making a new test calendar.

[tobixen]

Trying to run tests towards Google now - but it fails big time. Google does support creation of new calendars from the webui, but perhaps not through their caldav adapter (I'll try to google a bit on it).

[tobixen]

ref google, they do have an overview of what's supported on https://developers.google.com/calendar/caldav/v2/guide - MKCALENDAR is not supported.

(Also, VTODO is not supported - that's a pity, since they do support tasks from the webui).

[tobixen]

This was eventually fixed at some point. I believe. And also, radicale now supports mkcalendar, at least it works for me.