Fix for health checking info and slb real service page of Monitoring Center

Fix the tree of health check for SLB Virtual Service for Monitoring Center

1-1. There is no "connection_count" for L2IP protocal, so except it

1-2. Set 0 if the return data is null or none

1-3. Prevent KeyError exception
Fix the tree, histogram and datatable for SLB Real Service for Monitoring Center

2-1. Set rs_template to monitorable=True to show the name of health check

2-2. Call manager itself for L4L7RealService to prevent cache wrong problem

2-3. Add "Average Packets In Rate" and "Average Packets Out Rate" output fields