Fixes for gevent/gdrive

cps.py

@@ -11,19 +11,23 @@ sys.path.append(os.path.join(base_path, 'cps'))
 sys.path.append(os.path.join(base_path, 'vendor'))
 
 from cps import web
-from tornado.wsgi import WSGIContainer
-from tornado.httpserver import HTTPServer
-from tornado.ioloop import IOLoop
-from gevent.wsgi import WSGIServer
+try:
+    from gevent.wsgi import WSGIServer
+    gevent_present = True
+except ImportError:
+    from tornado.wsgi import WSGIContainer
+    from tornado.httpserver import HTTPServer
+    from tornado.ioloop import IOLoop
+    gevent_present = False
 
 if __name__ == '__main__':
     if web.ub.DEVELOPMENT:
         web.app.run(host="0.0.0.0", port=web.ub.config.config_port, debug=True)
     else:
-        try:
+        if gevent_present:
             web.app.logger.info('Attempting to start gevent')
             web.start_gevent()
-        except ImportError:
+        else:
             web.app.logger.info('Falling back to Tornado')
             http_server = HTTPServer(WSGIContainer(web.app))
             http_server.listen(web.ub.config.config_port)