Slave: Update TF-M jobs to use Bionic over Xenial

Signed-off-by: Karl Zhang <karl.zhang@arm.com>
Change-Id: Icf49df65bc80697b5e02aef1d18e863ff5187127
diff --git a/jenkins/build-config.jpl b/jenkins/build-config.jpl
index c62fbc9..60e04d7 100644
--- a/jenkins/build-config.jpl
+++ b/jenkins/build-config.jpl
@@ -9,9 +9,9 @@
 @Library('trustedfirmware') _
 import org.trustedfirmware.Gerrit
 
-def nodeLabel = "docker-amd64-xenial"
+def nodeLabel = "docker-amd64-bionic"
 if (env.COMPILER == "ARMCLANG") {
-  nodeLabel = "docker-amd64-xenial-armclang"
+  nodeLabel = "docker-amd64-bionic-armclang"
 }
 
 node(nodeLabel) {