Vendorise six.py

Because pyinstaller adds an old version to the path:

http://www.pyinstaller.org/ticket/773

fig/packages/docker/auth/auth.py

@@ -17,7 +17,7 @@ import fileinput
 import json
 import os
 
-import six
+from fig.packages import six
 
 from ..utils import utils
 

fig/packages/docker/client.py

@@ -19,7 +19,7 @@ import struct
 
 import requests
 import requests.exceptions
-import six
+from fig.packages import six
 
 from .auth import auth
 from .unixconn import unixconn

fig/packages/docker/unixconn/unixconn.py

@@ -11,7 +11,7 @@
 #    WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 #    See the License for the specific language governing permissions and
 #    limitations under the License.
-import six
+from fig.packages import six
 
 if six.PY3:
     import http.client as httplib

fig/packages/docker/utils/utils.py

@@ -17,7 +17,7 @@ import tarfile
 import tempfile
 
 import requests
-import six
+from fig.packages import six
 
 
 def mkbuildcontext(dockerfile):