[AIRFLOW-1594] Don't install test packages into python root.[]

By default `find_packages()` will find _any_ valid
python package,
including things under tests. We don't want to
install the tests
packages into the python path, so exclude those.

Closes apache#2597 from ashb/AIRFLOW-1594-dont-install-
tests

setup.py

@@ -202,7 +202,7 @@ def do_setup():
         description='Programmatically author, schedule and monitor data pipelines',
         license='Apache License 2.0',
         version=version,
-        packages=find_packages(),
+        packages=find_packages(exclude=['tests*']),
         package_data={'': ['airflow/alembic.ini', "airflow/git_version"]},
         include_package_data=True,
         zip_safe=False,