devserver: module import cleanup

* Import statements re-grouped: standard lib, third party,
  project-local; separated by a single line, preceded by a single line
  and followed by two lines. Each group is sorted alphabetically.

* Removed unused imports.

BUG=None
TEST=Passes unit tests.

Change-Id: Iee4f78b1256457bd19b2c159a29763ba3404c272
Reviewed-on: https://gerrit.chromium.org/gerrit/33859
Reviewed-by: Chris Sosa <sosa@chromium.org>
Commit-Ready: Gilad Arnold <garnold@chromium.org>
Tested-by: Gilad Arnold <garnold@chromium.org>
diff --git a/common_util.py b/common_util.py
index 967b09b..d4acccf 100644
--- a/common_util.py
+++ b/common_util.py
@@ -4,16 +4,16 @@
 
 """Helper class for interacting with the Dev Server."""
 
-import cherrypy
 import distutils.version
 import errno
-import lockfile
 import os
 import random
 import re
 import shutil
 import time
 
+import lockfile
+
 import build_artifact
 import gsutil_util
 import log_util