Change log_flush_frequency to use -

Since we have the rename, we don't need our declaration to look like
glog's.

pkg/util/logs.go

@@ -25,8 +25,7 @@ import (
 	"github.com/spf13/pflag"
 )
 
-// Uses _ instead of - to better align with glog flags.
-var logFlushFreq = pflag.Duration("log_flush_frequency", 5*time.Second, "Maximum number of seconds between log flushes")
+var logFlushFreq = pflag.Duration("log-flush-frequency", 5*time.Second, "Maximum number of seconds between log flushes")
 
 // TODO(thockin): This is temporary until we agree on log dirs and put those into each cmd.
 func init() {