Cleanup session object

If a session object is not provided to the get_http_client function (as
is done via osc), the glance client uses it's own HTTPClient class. This
class creates a session but does not properly close it when it is done.
This can lead to resource warnings about unclosed sockets. This change
adds a __del__() to the HTTPClient class to close out the session
correctly.

Change-Id: Idccff338fa84c46ca0e429bb533a2a5217205eef
Closes-Bug: #1838694

glanceclient/common/http.py

@@ -183,6 +183,15 @@ class HTTPClient(_BaseHTTPClient):
             self.session.cert = (kwargs.get('cert_file'),
                                  kwargs.get('key_file'))
 
+    def __del__(self):
+        if self.session:
+            try:
+                self.session.close()
+            except Exception as e:
+                LOG.exception(e)
+            finally:
+                self.session = None
+
     @staticmethod
     def parse_endpoint(endpoint):
         return netutils.urlsplit(endpoint)