e2e: Add caching to git repositories

It's very expensive to create new repositories from scratch. To avoid
this, a new repo & remotes are only created if necessary (depending on a
cache key given on request). If not created, they are simply copied from
a stored, clean repository / remote.

e2e_tests/conftest.py

@@ -1,8 +1,14 @@
 import os
 
+from helpers import *
+
 
 def pytest_configure(config):
     os.environ["GIT_AUTHOR_NAME"] = "Example user"
     os.environ["GIT_AUTHOR_EMAIL"] = "user@example.com"
     os.environ["GIT_COMMITTER_NAME"] = "Example user"
     os.environ["GIT_COMMITTER_EMAIL"] = "user@example.com"
+
+
+def pytest_unconfigure(config):
+    pass