Default m3msg write timeouts to 5 seconds (#2698)

This changes both the Producer sending new messages and the Consumer
sending ack messages.

5s is a safer default to prevent infinite blocking if the TCP connection
is not currently available for writing (i.e the buffer is full).

src/msg/consumer/options.go

@@ -33,8 +33,7 @@ var (
 	defaultAckBufferSize        = 1048576
 	defaultAckFlushInterval     = 200 * time.Millisecond
 	defaultConnectionBufferSize = 1048576
-	// TODO(ryanhall07): set this to 5s once we verify this works.
-	defaultWriteTimeout         = 0 * time.Second
+	defaultWriteTimeout         = 5 * time.Second
 )
 
 type options struct {

src/msg/producer/writer/options.go

@@ -43,7 +43,7 @@ const (
 
 	defaultNumConnections            = 4
 	defaultConnectionDialTimeout     = 5 * time.Second
-	defaultConnectionWriteTimeout    = time.Duration(0)
+	defaultConnectionWriteTimeout    = 5 * time.Second
 	defaultConnectionKeepAlivePeriod = 5 * time.Second
 	defaultConnectionResetDelay      = 2 * time.Second
 	defaultConnectionFlushInterval   = time.Second