Add UPDATE_TO_MYSQL57 flag to "Deploy - upgrade Galera cluster" job

PROD-36779

Change-Id: Ib9d215835ecf446154a27052e00ae73acb778d42
(cherry picked from commit ba9966bf00d258b105dbe7da74c4b310f48e7891)
diff --git a/jenkins/client/job/deploy/update/upgrade_galera.yml b/jenkins/client/job/deploy/update/upgrade_galera.yml
index 8864529..8ebaf51 100644
--- a/jenkins/client/job/deploy/update/upgrade_galera.yml
+++ b/jenkins/client/job/deploy/update/upgrade_galera.yml
@@ -27,6 +27,10 @@
             SALT_MASTER_CREDENTIALS:
               type: string
               default: "salt"
+            UPDATE_TO_MYSQL57:
+              type: boolean
+              default: 'false'
+              description: "Set this flag if you are updating MySQL from 5.6 to 5.7"
             SHUTDOWN_CLUSTER:
               type: boolean
               default: 'false'