added configuration 'http_proxy' to allow the usage of a proxy

configuration.py

@@ -82,13 +82,14 @@ class ConfigurationObject(object):
         # check host name
         # Set this to True/False to enable/disable SSL hostname verification.
         self.assert_hostname = None
-
         # urllib3 connection pool's maximum number of connections saved
         # per pool. Increasing this is useful for cases when you are
         # making a lot of possibly parallel requests to the same host,
         # which is often the case here.
         # When set to `None`, will default to whatever urllib3 uses
         self.connection_pool_maxsize = None
+        # http proxy setting
+        self.http_proxy_url = None
 
         # WebSocket subprotocol to use for exec and portforward.
         self.ws_streaming_protocol = "v4.channel.k8s.io"

rest.py

@@ -106,9 +106,14 @@ class RESTClientObject(object):
             kwargs['assert_hostname'] = config.assert_hostname
 
         # https pool manager
-        self.pool_manager = urllib3.PoolManager(
-            **kwargs
-        )
+        if config.http_proxy_url is not None:
+            self.pool_manager = urllib3.proxy_from_url(
+                config.http_proxy_url, **kwargs
+            )
+        else:
+            self.pool_manager = urllib3.PoolManager(
+	        **kwargs
+            )
 
     def request(self, method, url, query_params=None, headers=None,
                 body=None, post_params=None, _preload_content=True,