[ci] do not fail on Docker build failure

Since the docker image is only experimentally supported and causing
build errors, we only attempt to build it but don't fail when it fails.

Signed-off-by: Timothy Trippel <ttrippel@google.com>
diff --git a/azure-pipelines.yml b/azure-pipelines.yml
index 610d34f..6820c8a 100644
--- a/azure-pipelines.yml
+++ b/azure-pipelines.yml
@@ -647,6 +647,7 @@
   - template: ci/checkout-template.yml
   - task: Docker@2
     displayName: Build Developer Utility Container
+    continueOnError: True
     inputs:
       command: build
       Dockerfile: ./util/container/Dockerfile