don't start Xvfb for each run

[fippo]

it seems Xvfb doesn't like to be started often so the strategy from turn-prober is bad when running under cron / continually.

@stongo

[fippo]

i wonder if test-cron should start Xvfb or if we should also assume it is running under Xvfb with $DISPLAY set appropriately... @bear @stongo?

[bear]

my ops side says that it should expect it to be present and look for $DISPLAY - this would let it also be able to be run inside of a normal XWindow environment

[fippo]

this is how the tester now behaves. the "cron" thing is built for automation however.

[bear]

lets make the cron script look for $DISPLAY and then start Xvfb if required