display friendly error message on handshake error (go-mysql-org#435)

Author: dhlin

client/auth.go

@@ -34,7 +34,7 @@ func (c *Conn) readInitialHandshake() error {
 }
 
 if data[0] == ERR_HEADER {
-return errors.New("read initial handshake error")
+return errors.Annotate(c.handleErrorPacket(data), "read initial handshake error")
 }
 
 if data[0] < MinProtocolVersion {