Switch to glog for logging, bridge logging to glog.

1) imported glog to third_party (previous commit)
2) add support for third_party/update.sh to update just one pkg
3) search-and-replace:
  s/log.Printf/glog.Infof/
  s/log.Print/glog.Info/
  s/log.Fatalf/glog.Fatalf/
  s/log.Fatal/glog.Fatal/
4) convert glog.Info.*, err into glog.Error*

Adds some util interfaces to logging and calls them from each cmd, which will
set the default log output to write to glog.  Pass glog-wrapped Loggers to
etcd for logging.

Log files will go to /tmp - we should probably follow this up with a default
log dir for each cmd.

The glog lib is sort of weak in that it only flushes every 30 seconds, so we
spin up our own flushing goroutine.