Add millisecond precision to nsjail logs

[phoebetse]

I'd like to see logs with timestamps with millisecond precision.

I'm not super familiar with C++, but I think https://github.com/google/nsjail/blob/master/util.cc#L311 is where the change would need to be. It looks like the timeToStr utility function is outputting a string to second precision, so maybe using something like gettimeofday as mentioned on stackexchange would work?

Would a change like this make sense? If so, I'm happy to take a stab at it.

[disconnect3d]

Hi,

I think it would make sense and while I am not a maintainer, I think it may get merged :P.