pcap should work w/o requiring a window system #79
Description
Currently using --pcap requires using run_in_window. But using packet captures for actual testing is actually a great feature we should have. We need a way to start and stop packet captures using a popen()d process.
When building this keep in mind that we also want to create a way to popen processes in mutest eventually that also clean themselves up so this solution should work with that in mind as well. We don't need to solve that problem here, but should think that we may want to use the same method to start a pcap that way that would automatically be cleaned up at the end of the mutest that launched it. Maybe that's just using popen() still but just consider it.
We should probably use this popen() all the time and use a tail -F in a run_in_window() for user interactive use.
When this is done we need tests of pcap functionality for all, network and node:intf.