Use oslo-config-2013.1b3

The cfg API is now available via the oslo-config library, so switch to
it and remove the copied-and-pasted version.

Add the 2013.1b3 tarball to tools/pip-requires - this will be changed
to 'oslo-config>=2013.1' when oslo-config is published to pypi. This
will happen in time for grizzly final.

Add dependency_links to setup.py so that oslo-config can be installed
from the tarball URL specified in pip-requires.

Remove the 'deps = pep8==1.3.4' from tox.ini as it means all the other
deps get installed with easy_install which can't install oslo-config
from the URL.

Excluded code from oslo-incubator in the pep8 check.

Retain dummy cfg.py file until keystoneclient middleware has been
updated (I18c450174277c8e2d15ed93879da6cd92074c27a).

Change-Id: I4815aeb8a9341a31a250e920157f15ee15cfc5bc
Merge "Use oslo-config-2013.1b3"