chart xshape tests are now enabled on @50 tinderbox

Hey,

so the chart XShape tests are enabled again on the @50 tinderbox. They test
the layout and rendering of charts and are therefore the missing piece
besides the import and export tests in chart2. Sadly we can't push them to
more machines as the chart layout is not the same on each machine. They
have been enabled for a short period in the past on all machines but there
have been so many problems with small rendering differences between
different machines that I decided this time to limit the test for now to a
single tinderbox.

There is now no excuse anymore to not add a test when you fix a bug in
chart2 unless it is for the dialogs. Please help me avoid such embarrassing
bugs like fdo#75075 in the future in chart2.

I will use that tinderbox in the future for more exotic tests that I can't
or don't want to enable by default so don't be surprised if you see the
tinderbox complain in tests that are not executed locally.

Regards,
Markus