Mark individual step as failure

When investigating a problem it is usually more important to know
which individual step failed, than knowing the difference between
"tests failing" and "failed to build". Therefore use Jenkins "error"
command instead of marking the whole pipeline as "UNSTABLE".

Change-Id: Ia14be4e8c76062e142523f6d01417b0f6522036f
diff --git a/jenkins/lib/src/build/bazel/ci/BazelUtils.groovy b/jenkins/lib/src/build/bazel/ci/BazelUtils.groovy
index e10236f..86db30b 100644
--- a/jenkins/lib/src/build/bazel/ci/BazelUtils.groovy
+++ b/jenkins/lib/src/build/bazel/ci/BazelUtils.groovy
@@ -127,8 +127,7 @@
         def status = bazelCommand("test ${filteredTests.replaceAll("\n", " ")}", true)
         if (status == 3) {
           // Bazel returns 3 if there was a test failures but no breakage, that is unstable
-          script.currentBuild.result = "UNSTABLE"
-          script.echo("`bazel test` returned status 3 which indicates test failures")
+          script.error("`bazel test` returned status 3 which indicates test failures")
         } else if (status != 0) {
           // TODO(dmarting): capturing the output mark the wrong step at failure, there is
           // no good way to do so, it would probably better to have better output in the failing