Start the watcher after handshake (go-sql-driver#627)

Fixes go-sql-driver#626

Author: shogo82148

driver.go

@@ -66,11 +66,6 @@ func (d MySQLDriver) Open(dsn string) (driver.Conn, error) {
 	mc.parseTime = mc.cfg.ParseTime
 	mc.strict = mc.cfg.Strict
 
-	// Call startWatcher for context support (From Go 1.8)
-	if s, ok := interface{}(mc).(watcher); ok {
-		s.startWatcher()
-	}
-
 	// Connect to Server
 	if dial, ok := dials[mc.cfg.Net]; ok {
 		mc.netConn, err = dial(mc.cfg.Addr)
@@ -92,6 +87,11 @@ func (d MySQLDriver) Open(dsn string) (driver.Conn, error) {
 		}
 	}
 
+	// Call startWatcher for context support (From Go 1.8)
+	if s, ok := interface{}(mc).(watcher); ok {
+		s.startWatcher()
+	}
+
 	mc.buf = newBuffer(mc.netConn)
 
 	// Set I/O timeouts