[Windows] Working unit tests for certbot-nginx (#6782)

This PR fixes certbot-nginx and relevant tests to make them succeed on Windows.

Next step will be to enable integration tests through certbot-ci in a future PR.

* Fix tests and incompabilities in certbot-nginx for Windows

* Fix lint, fix oldest local dependencies

tox.cover.py

@@ -35,7 +35,8 @@ COVER_THRESHOLDS = {
 }
 
 SKIP_PROJECTS_ON_WINDOWS = [
-    'certbot-apache', 'certbot-nginx', 'certbot-postfix', 'letshelp-certbot']
+    'certbot-apache', 'certbot-postfix', 'letshelp-certbot']
+
 
 def cover(package):
     threshold = COVER_THRESHOLDS.get(package)['windows' if os.name == 'nt' else 'linux']
@@ -54,6 +55,7 @@ def cover(package):
         sys.executable, '-m', 'coverage', 'report', '--fail-under', str(threshold), '--include',
         '{0}/*'.format(pkg_dir), '--show-missing'])
 
+
 def main():
     description = """
 This script is used by tox.ini (and thus by Travis CI and AppVeyor) in order
@@ -77,5 +79,6 @@ Option -e makes sure we fail fast and don't submit to codecov."""
     for package in packages:
         cover(package)
 
+
 if __name__ == '__main__':
     main()