prepare utils for pypi distribution (GoogleCloudPlatform#5848)

* prepare utils for pypi distribution

* address setup.py nits

Author: leahecole

composer/dag_test_utils/README.md

@@ -6,7 +6,7 @@ This package is used internally to unit test the validity of all Cloud Composer
 
 Add the following to your `requirements-test.txt` file:
 
-`git+https://github.com/GoogleCloudPlatform/python-docs-samples.git#egg=dag_test_utils&subdirectory=composer/dag_test_utils`
+`cloud_composer_dag_test_utils`
 
 Import the internal unit testing module
 

composer/dag_test_utils/pyproject.toml

@@ -0,0 +1,3 @@
+[build-system]
+requires = ["setuptools", "wheel"]
+build-backend = "setuptools.build_meta"

composer/dag_test_utils/setup.py

@@ -16,12 +16,12 @@
 from setuptools import setup
 
 setup(
-    name="dag_test_utils",
+    name="cloud_composer_dag_test_utils",
     version="0.0.1",
-    url="git@github.com:GoogleCloudPlatform/python-docs-samples.git#egg=dag_test_utils&subdirectory=composer/dag_test_utils",
-    author="Google Cloud Platform",
-    description="Utility used to unit test example Apache Airflow DAGs",
+    url="https://github.com/GoogleCloudPlatform/python-docs-samples/tree/master/composer/dag_test_utils",
+    author="Google LLC",
+    description="Utility used to unit test example Apache Airflow DAGs for Google Cloud Composer. This is not an officially supported Google product.",
     packages=find_packages(),
     py_modules=['internal_unit_testing'],
-    install_requires=['apache-airflow[gcp]']
+    install_requires=['apache-airflow[google]==1.10.15']
 )