[jsonchecker] Remove const from parameters

In 62957f104 we changed the
Retries and RetryDelay from var to const. This patch reverst that change
as we may need to adjust them based on the test needs.

Signed-off-by: Anastasios Papagiannis <tasos.papagiannnis@gmail.com>

pkg/jsonchecker/jsonchecker.go

@@ -20,7 +20,7 @@ import (
 	"github.com/sirupsen/logrus"
 )
 
-const (
+var (
 	Retries    = 13
 	RetryDelay = 3 * time.Second
 )