Saves the session variables to a file so that the same analysis can be continued later.

def do_save(self, arg):
        """Saves the session variables to a file so that the same analysis can be continued later."""
        #We need to save the full paths to the staging directories for the tests that are loaded
        #so far; then when the session is restored, we can reparse the results.
        from os import path
        import json
        fullpath = path.expanduser(arg)

        data = {
            "tests": [path.abspath(a.stagedir) for a in list(self.tests.values())],
            "args": self.args
        }

        with open(fullpath, 'w') as f:
            json.dump(data, f)
        msg.okay("Saved current session to {}".format(fullpath))