This commit consists of:
1) Add session management to netconf
2) Modularize the rpc call
3) Improve the error handling
4) Small bug fixes

Change-Id: I023edb76e3743b633ac87be4967d656e09e2b970
diff --git a/netconf/session/session_mgr.py b/netconf/session/session_mgr.py
new file mode 100644
index 0000000..ee4382f
--- /dev/null
+++ b/netconf/session/session_mgr.py
@@ -0,0 +1,47 @@
+#!/usr/bin/env python
+#
+# Copyright 2016 the original author or authors.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#      http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+#
+from session import Session
+import structlog
+
+log = structlog.get_logger()
+
+class SessionManager:
+    instance = None
+
+    def __init__(self):
+        self.next_session_id = 1
+        self.sessions = {}
+
+    def create_session(self, user):
+        session = Session(self.next_session_id, user)
+        self.sessions[self.next_session_id] = session
+        self.next_session_id += 1
+        return session
+
+    def remove_session(self, session):
+        session_id = session.session_id
+        if session_id in self.sessions.keys():
+            del self.sessions[session_id]
+            log.info('remove-session', session_id=session_id)
+        else:
+            log.error('invalid-session', session_id=session_id)
+
+
+def get_session_manager_instance():
+    if SessionManager.instance == None:
+        SessionManager.instance = SessionManager()
+    return SessionManager.instance
\ No newline at end of file