The motivation is to free us of a reliance on a rather modern version of setuptools, which caused le-auto failures for people on Wheezy and other older distros. (The alternative would have been to forcibly upgrade setuptools as the old le-auto did, but less is more.)
Mock is used only in tests, so we move it to tests_require. It will still be installed automatically when setup.py test is run. Give all packages a test_suite so this works.
The "testing" extra remains for optional packages not required for the nose tests but used in tox. However, the extra is much less useful now and is a candidate for deletion. We could roll the list of packages therein into the tox config so as not to favor any particular package.
Remove tests_require=install_requires, which I don't think does anything useful, since install requirements are implicitly installed when running setup.py test.
Fix tests to pass with mock removed. We had to stop them pulling down LE from PyPI, since the current version there (0.1.1) requires mock and explodes when `letsencrypt` is run.
