fixture teardown: Wait for the a11y bus launcher to really die
fixture teardown: Wait for the a11y bus launcher to really die

I think the failed CI jobs are due to at-spi-bus-launcher taking an
unspecified amount of time to die after the Logout call.  So, let's
wait for it.

GNOME/at-spi2-core,GNOME/at-spi2-core,GNOME/at-spi2-core