Set the bazel verison to 0.28.1 explicitly (envoyproxy#8037)

In theopenlab/openlab-zuul-jobs#622 , the OpenLab add the ability to set the bazel to specific version explicitly. This patch add the bazel role for the envoy job.

Signed-off-by: Yikun Jiang <[email protected]>

Author: Yikun

.zuul/playbooks/envoy-build/run.yaml

@@ -3,6 +3,8 @@
   roles:
     - role: config-gcc
       gcc_version: 7
+    - role: config-bazel
+      bazel_version: 0.28.1
   tasks:
     - name: Build envoy
       shell: