Perform a sync with oslo-incubator.

Perform a sync with oslo-incubator.

This oslo-incubator sync pulls in a new log.py which will make quantum's
default log output format the same as nova, glance and cinder (once
cinder's corresponding oslo sync merges). This common log format
simplifies log indexing as part of CI and makes lives easier for
deployers.

This sync does add a requirement on six as jsonutils depends on it. It
updates install_venv_common.py to be python26 compatible. It also brings
in a bunch of recent python3 compatibility that was added to oslo.

Fixes bug 1183144

Change-Id: Id0f196d7b5680e5950e4a27d66042bf00ccd49e6