Fix inclusion of tests package in setup.py (#131)

Author: Jon Wayne Parrott

MANIFEST.in

@@ -1,3 +1,2 @@
-include README.rst
-graft google
-global-exclude *.pyc __pycache__
+include README.rst LICENSE CHANGELOG.rst
+recursive-include tests *

setup.py

@@ -39,7 +39,7 @@
     description='Google Authentication Library',
     long_description=long_description,
     url='https://github.com/GoogleCloudPlatform/google-auth-library-python',
-    packages=find_packages(exclude=('tests', 'system_tests')),
+    packages=find_packages(exclude=('tests*', 'system_tests*')),
     namespace_packages=('google',),
     install_requires=DEPENDENCIES,
     extras_require={