Exit node retrying: Retry 3 times. Also add tests for it.

Closes #20

Signed-off-by: Jesús <heckyel@hyperbola.info>

tests/conftest.py

@@ -0,0 +1,14 @@
+import pytest
+import urllib3
+import urllib
+import urllib.request
+import socket
+
+# https://realpython.com/pytest-python-testing/
+@pytest.fixture(autouse=True)
+def disable_network_calls(monkeypatch):
+    def stunted_get(*args, **kwargs):
+        raise RuntimeError('Network access not allowed during testing!')
+    monkeypatch.setattr(urllib.request, 'Request', stunted_get)
+    monkeypatch.setattr(urllib3.PoolManager, 'request', stunted_get)
+    monkeypatch.setattr(socket, 'socket', stunted_get)