docker.py: Python 2.6 argparse compatibility

Add the scripts/ directory to sys.path so Python 2.6 will be able to
import argparse.

Cc: Fam Zheng <famz@redhat.com>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Acked-by: John Snow <jsnow@redhat.com>
Acked-by: Fam Zheng <famz@redhat.com>
Message-id: 20170825155732.15665-3-stefanha@redhat.com
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>

tests/docker/docker.py

@@ -13,12 +13,14 @@
 
 import os
 import sys
+sys.path.append(os.path.join(os.path.dirname(__file__),
+                             '..', '..', 'scripts'))
+import argparse
 import subprocess
 import json
 import hashlib
 import atexit
 import uuid
-import argparse
 import tempfile
 import re
 import signal