re-worked appender to use jedis connection pooling and newer version. Th...

I re-worked the code to use the newer jedis plugin, and use the JedisPool implementation for connection management. I added some robustness to connection testing/quality. It seems 

This is to avoid the problem where the application thinks it is connected but is not actually connected. ( I am seeing this a lot). Apparently connection.isConnected() is not that good of a check if it's actually connected.