implement connection pool with fail-over, health check and rebind interval

[kortemik]

implement connection pool with fail-over, health check and rebind interval

• connection pool janitor thread should monitor the liveness of the pool by opening and closing the relp connection at configured intervals.
• active connection should rebind after configured number of records sent.
• fail-over and rebind should pick randomly a connection from the pool that has last health check as passed.