Adding check that **all** setup.py README's are valid RST. (#3318)

* Adding check that **all** setup.py README's are valid RST.

Follow up to #3316. Fixes #2446.

* Fixing duplicate reference in Logging README.

* Fixing duplicate reference in Monitoring README.

google-cloud-speech/nox.py

@@ -77,6 +77,15 @@ def lint(session):
     session.run('flake8', 'google/cloud/speech')
 
 
+@nox.session
+def lint_setup_py(session):
+    """Verify that setup.py is valid (including RST check)."""
+    session.interpreter = 'python3.6'
+    session.install('docutils', 'Pygments')
+    session.run(
+        'python', 'setup.py', 'check', '--restructuredtext', '--strict')
+
+
 @nox.session
 def cover(session):
     """Run the final coverage report.