[FAB-5359] Add BroadcastResponse info to proto

The BroadcastResponse proto currently only returns a single status
field.  This was of course intentional, as clients should be utilizing
the status field for any programatic decisions, such as retrying or not.

However, from a usability perspective, diagnosing user error from only a
status code can be quite difficult.  Was the request bad because the
message was malformed, or because it attempted an illegal operation?

This CR simply adds a new proto field named 'info', to the
BroadcastResponse proto.  This info field is a string which may be
populated with human readable text.

There is no guarantees made about the stability of this text (the error
text may change from version to version), and clients should continue to
utilize the status field for any programatic decisions.

Although this is a proto change, it is both forwards and backwards
compatible.  v1.0.x clients will be able to receive BroadcastResponses
made by a v1.1.x server, and v1.1.x clients will see an unpopulated info
field from v1.0.x servers.

Change-Id: Ie4f227285454fab1b6794eaacdaefa42549fff23
Signed-off-by: Jason Yellick <jyellick@us.ibm.com>

Author: Jason Yellick

protos/orderer/ab.pb.go

@@ -24,7 +24,10 @@ option java_package = "org.hyperledger.fabric.protos.orderer";
 package orderer;
 
 message BroadcastResponse {
+    // Status code, which may be used to programatically respond to success/failure
     common.Status status = 1;
+    // Info string which may contain additional information about the status returned
+    string info = 2;
 }
 
 message SeekNewest { }