NA-2045 Sharing connections between various instances of HecubaClientMan...

...ager:

-After moving to datastax we can connect to multiple column family and key spaces using same session and cluster respectively.
-It is the recommended way of using the driver.
-This patch includes changes for cluster and session sharing between multiple HecubaClientManager instances.
I would still synchronize this since there is a chance that later code snippets can be introduced to access this. Also, making this synchronized won't have any perf impact when its called from getSession since its reentrant.