[osx] get secondary DNS

this PR will get secondary DNS on osx. Sleep(100); is added as popen takes sometime to finish.
O think the real solution is to know somehow that the popened process was finished. ATM this is doable by calling pclose (which is a bummer because afterwards we know the process is done - but we can't read from the pipe anymore :) ). I think we have this problem on all our popen calls (where we have luck that the call is quick enough).

If you find out a way to tell if the forked process (popen will fork it for us) is finished before reading from the pipe this would be the best solution. If not the Sleep might be the only solution for now.

@davilla any idea? Popen is a bit of a bitch for our use case here imo.