This commit enables the VirtualBox graphics adapter, provides guest mouse
pointer integration with Nitpicker using the 'vbox_pointer' application
and enhances the VirtualBox run scripts with the configuration of
Nitpicker, input merger and network driver.
Fixes#1474
Some functions in the time manager, for example 'TMTimerSet()' and
'TMTimerStop()' let VirtualBox abort with a failed assertion if the timer
does not change to a 'stable' state after 1000 calls of a mixture of
'yield' and 'sleep'. On Genode, this happens sometimes when the 'EMT'
thread is executing 'TMTimerSet()' and gets interrupted by the 'TAP'
thread, which calls 'TMTimerStop()' and waits for the 'EMT' thread to
finish setting the timer. Since the 'EMT' thread has the lowest priority,
1000 retries can be too few. Without the assertion, these functions would
return an error code, which is often ignored by the caller, so it seems
safer to keep retrying until the function can return successfully.
Fixes#1437
