btsocket: use setuptools rather than distutils

This gives us the bdist_egg command that autotest needs.

BUG=chromium:348704
TEST=python setup.py bdist_egg

Change-Id: I7a1d0292a00858e3485b9aee74b6dc898334031b

setup.py

diff --git a/setup.py b/setup.py
index aed456c..47761d6 100644
--- a/setup.py
+++ b/setup.py
@@ -2,7 +2,7 @@
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
-from distutils.core import setup, Extension
+from setuptools import setup, Extension
 
 ext1 = Extension('btsocket._btsocket', sources=['src/btsocket.c'])