bionic-amd64-tf-a-build: Switch to Java 11

The latest Jenkins releases support only Java 11 (on the server side, and
thus on the build agent side, as the versions should match).

Signed-off-by: Paul Sokolovsky <paul.sokolovsky@linaro.org>
Change-Id: Iacea4c08f8fa50935ed28e730b16a729330c325d
diff --git a/bionic-amd64-tf-a-build/Dockerfile b/bionic-amd64-tf-a-build/Dockerfile
index 08bf54d..2d70f88 100644
--- a/bionic-amd64-tf-a-build/Dockerfile
+++ b/bionic-amd64-tf-a-build/Dockerfile
@@ -32,7 +32,7 @@
     libxml-libxml-perl \
     lld \
     locales \
-    openjdk-8-jdk \
+    openjdk-11-jre-headless \
     openssh-server \
     perl \
     python \