UprFeed is implemented as a genServer routine.

This avoids race condition bugs.
- race-condition: sending on a closed channel (output channel).
- race-condition: async access over connPools.
- UprFeed opens a connection with all kvnodes, application like projector
  will be co-located and will connect with local-node.
- projector does not need connection retry.
- bug-fix: to close gomemcached connection after GetFailoverLogs() call.
- using sync.WaitGroup{} to synchronize feed closing.