Check for a pid rather than connected property of process before killing.

Because the 'connected' property of the spawned phantom process was always false, it was left behind when running tests with grunt-contrib-qunit on Mac OS X10.9.2.  Checking for a pid and not the connected property of the process addressed the problem.  Its possible this might address https://github.com/gruntjs/grunt-contrib-qunit/issues/60.