Merge "Connection Manager infrastructure supporting the Clustering Active-Active...

Merge "Connection Manager infrastructure supporting the Clustering Active-Active requirement. This commit brings in the following changes : 1. Connection Manager as a functional module that runs above SAL providing common services to various south-bound plugins.    The initial version of Connection Manager takes in Node as the only argument and let the Connection Management Scheme to determine the fate of the connection.    Primary use-case that is addressed here is the HA/Clustering's Active-Active mode with the ability for Nodes to connect to different controller in a cluster."