ClockDrift test failures on Windows (OAK-1904)

[Julian Reschke]

So,

as they plague the new Jenkins build and they also occur sometimes over 
here, I spent some time with them...

1) There was a single test for all of the clocks (simple, accurate, 
fast); I have refactored these so that they execute separately.

2) Most of the failures seem to be related to Clock.Fast. This is a 
clock that relies on Clock.ACCURATE and a regular (10ms) update from 
that clock. At least on my platform, I can see that if the updates 
occur, they actually happen every 15ms (not 10ms).

Thoughts:

- we need to find out whether the actual code fails, or whether it's a 
problem in the test case

- Relying on a scheduled thread to be executed in precise intervals 
seems like asking for trouble

- As far as I can tell, the reason why we even have Clock.Fast is the 
assumption that Clock.SIMPLE (== System.currentTimeMillis()) may be 
"slow". Does anybody know what exactly is the problem? (Because, after 
all, the simplest possible fix would be to get rid of this apparently 
fragile code)

Best regards, Julian