Use tests_require to fill in test requirements in the setuptools template

This lets me specify test specific dependencies without modifying the meta.yaml
template by simply adding "tests_require" to my setup.py file, e.g.,

	from setuptools import setup, find_packages

	setup(
	    name="dummy_package",
	    version="0.0.1.abc",
	    packages=find_packages(),
	    tests_require=['nose'],
	)

I use this so I can run my tests with nose.

There are other setuptools specific keywords (such as "install_requires") that
it might also be worth supporting in the default template:
https://pythonhosted.org/setuptools/setuptools.html#new-and-changed-setup-keywords

Another example would be the "test_suite" keyword, which if provided could signal
conda to run tests via `setup.py test` instead of run_tests.py.
Merge pull request #107 from shoyer/test_requires

Use tests_require to fill in test requirements in the setuptools template