server failures: fix handling of failing and timed out servers
server failures: fix handling of failing and timed out servers

There were several different bugs here:

* omcache_poll_fds() had inverted logic for calculating connection timeouts

* omcache_poll_fds() did not consider connection timeout, now it resets
  connections if connect_timeout has passed and the last attempt failed

* servers weren't being disabled after connecting to all available addresses
  failed, causing clients to keep slowly trying to connect to failed servers

* make sure to zero out req_count and value_count if either of them is empty

* don't log one entry for each disabled entry in ketama

ohmu/omcache,CrowdStrike/omcache,CrowdStrike/omcache,thedrow/omcache,ohmu/omcache,thedrow/omcache