[INTEGRATION] Build xtesting test images with 'istanbul' tag

Xtesting images should be also builded for 'istanbul' branch.
Images should be tagged 'istanbul'

Issue-ID: TEST-372
Signed-off-by: Michal Jagiello <michal.jagiello@t-mobile.pl>
Change-Id: I5a3231207469bb6b7bfcb4cbfeba6dc529d47442
diff --git a/jjb/integration/xtesting/integration-xtesting.yaml b/jjb/integration/xtesting/integration-xtesting.yaml
index a5674e2..0836168 100644
--- a/jjb/integration/xtesting/integration-xtesting.yaml
+++ b/jjb/integration/xtesting/integration-xtesting.yaml
@@ -39,6 +39,8 @@
       stream:
           - 'master':
                 branch: 'master'
+          - 'istanbul':
+                branch: 'istanbul'
           - 'honolulu':
                 branch: 'honolulu'
 
@@ -119,6 +121,9 @@
       - 'master':
             branch: 'master'
             files: ''
+      - 'istanbul':
+            branch: 'istanbul'
+            files: ''
       - 'honolulu':
             branch: 'honolulu'
             files: ''