Add requests.ConnectionError to watcher retries

Apparently with switch to Python 3, requests library raises a different
exception when read time out occurrs and it's quite general
requests.ConnectionError. This causes tracebacks like [1] to show up in
logs.

This is pretty scary for the user, so this commit suppresses those exceptions
and adds them to the list of exceptions K8sClient restarts watching.

[1] http://paste.openstack.org/show/786574/

Change-Id: I09f3803edffbe2ea5f1913238adc23212a323100

kuryr_kubernetes/k8s_client.py

@@ -271,7 +271,8 @@ class K8sClient(object):
                             # At this point it's safely passed to handler.
                             m = line_dict.get('object', {}).get('metadata', {})
                             resource_version = m.get('resourceVersion', None)
-            except (requests.ReadTimeout, ssl.SSLError) as e:
+            except (requests.ReadTimeout, requests.ConnectionError,
+                    ssl.SSLError) as e:
                 if isinstance(e, ssl.SSLError) and e.args != ('timed out',):
                     raise