Reduce requests connection pool size

Requests defaults to keeping 10 connections to the API alive. This
seems excessive, reduce it to 2.

Change-Id: Iac67fd4d855388d2671da3b7258b31d1eead77a9

ironic_python_agent/ironic_api_client.py

@@ -33,7 +33,15 @@ class APIClient(object):
     def __init__(self, api_url, driver_name):
         self.api_url = api_url.rstrip('/')
         self.driver_name = driver_name
+
+        # Only keep alive a maximum of 2 connections to the API. More will be
+        # opened if they are needed, but they will be closed immediately after
+        # use.
+        adapter = requests.adapters.HTTPAdapter(pool_connections=2,
+                                                pool_maxsize=2)
         self.session = requests.Session()
+        self.session.mount(self.api_url, adapter)
+
         self.encoder = encoding.RESTJSONEncoder()
         self.log = log.getLogger(__name__)
 

ironic_python_agent/tests/agent.py

@@ -53,6 +53,7 @@ class TestHeartbeater(test_base.BaseTestCase):
     def setUp(self):
         super(TestHeartbeater, self).setUp()
         self.mock_agent = mock.Mock()
+        self.mock_agent.api_url = 'https://fake_api.example.org:8081/'
         self.heartbeater = agent.IronicPythonAgentHeartbeater(self.mock_agent)
         self.heartbeater.api = mock.Mock()
         self.heartbeater.hardware = mock.create_autospec(