Fix & organize imports

Author: immerrr

splash/benchmark/benchmark.py

@@ -15,7 +15,7 @@
 from multiprocessing.pool import ThreadPool
 
 import requests
-from splash.file_server import serve_files
+from splash.benchmark.file_server import serve_files
 from splash.tests.utils import SplashServer
 
 PORT = 8806

splash/benchmark/download_sites.py

@@ -1,12 +1,13 @@
-from splash.tests.stress import lua_runonce
-
+import json
 import re
+import subprocess
 from urlparse import urlsplit
-import json
+
 from lxml import html
+
 import w3lib.html
-import subprocess
-from splash.file_server import serve_files
+from splash.benchmark.file_server import serve_files
+from splash.tests.stress import lua_runonce
 
 script_html = """
 function main(splash)