Introduce files from openstack common.

Introduce files from openstack common.

Because the openstack common project does not stick to latest pep8 rules,
I have to exclude some bad-ruled files in the tox.ini and run_tests.sh.
However pep8 does not support exclude option in the format quantum/openstack/common,
so I have to exclude some of openstack common files one by one.

Also, I have changed the Qunatum Context to base on the common context.

I does not update the setup.py in our openstack common dir and the one
under quantum top dir, since it should be maintained in a consistent way
across all of openstack projects.

After this introduction, we are ready for notification feature.

Change-Id: I2729c2dc3958835374c88d704e842e613785ec14