Use openci-testing branch

Change-Id: I20c24374b2ba46e707b71eb8ec2e804ea67b0ccb
diff --git a/mbedtls-dockerfile-builder.yaml b/mbedtls-dockerfile-builder.yaml
index 3bc6879..12158e4 100644
--- a/mbedtls-dockerfile-builder.yaml
+++ b/mbedtls-dockerfile-builder.yaml
@@ -5,7 +5,7 @@
     dsl: |-
       timestamps {
           stage('build-dockerfiles') {
-              node('dockerfile-builder') {
+              node('mbedtls-dockerfile-builder') {
                   dir('src') {
                       deleteDir()
                       checkout([