openstack/swift - swift - OpenDev: Free Software Needs Free Tools

The jenkins coverage jobs expect there to be a .coverage file, so deleting
it is a bad idea. Also, coverage erase will do that for us.
While we're in there, update tox.ini and setup.cfg to the latest.
Change-Id: Icd0a8fc66a5146e0d94f62a9f65a4536981d2916

* Adds tox config
 - based on the config from python-quantumclient and updated for
 test, pep8 and coverage execution as per nova's run_tests.sh.
 * Adds nosetests defaults in setup.cfg
 * Adds runtime dependencies in tools/pip-requires
 - dependencies were gathered by referencing the packages used in
 creation of a Swift All In One. Versions were determined by
 checking the swift-core/trunk ppa or, failing that, the version
 available in lucid.
 * Adds test dependencies in tools/test-requires
 * Updates swift/common/middleware/formpost.py for pep8 compliance
 * Adds instructions for executing the tests with Tox to the
 developer_guidelines
 * Adds instructions for installing openstack.nose_plugin to
 developer_saio
 * Fixes bug 909177
Change-Id: I5407924d2181e9ab335aaf76bf30c8d40deccbb4