Use Java 8 local toolchain for builds and tests

Check for Java 8 compatibility when validating incoming
changes. This is needed for preventing Java 11 -only changes
to pass validation without being Java 8 compatible.

Change-Id: Ifd8132d91f4bb9a8b80dd7b938c5fb6f6697f0c8
diff --git a/roles/bazelisk-build/tasks/main.yaml b/roles/bazelisk-build/tasks/main.yaml
index 71f0e31..b16cb42 100644
--- a/roles/bazelisk-build/tasks/main.yaml
+++ b/roles/bazelisk-build/tasks/main.yaml
@@ -2,14 +2,14 @@
   shell: |
     java -fullversion
     {{ bazelisk_executable }} version
-    {{ bazelisk_executable }} build --spawn_strategy=standalone --genrule_strategy=standalone {{ bazelisk_targets }}
+    {{ bazelisk_executable }} build --spawn_strategy=standalone --genrule_strategy=standalone --java_toolchain=//tools:error_prone_warnings_toolchain {{ bazelisk_targets }}
   args:
     executable: /bin/bash
     chdir: "{{ zuul_work_dir }}"
 - name: Run bazelisk test
   when: "bazelisk_test_targets != ''"
   shell: |
-    {{ bazelisk_executable }} test {{ bazelisk_test_targets }}
+    {{ bazelisk_executable }} test --java_toolchain=//tools:error_prone_warnings_toolchain {{ bazelisk_test_targets }}
   args:
     executable: /bin/bash
     chdir: "{{ zuul_work_dir }}"