Re-enable yaml end to end tests

Verifying the pipelinerun example worked was disabled due to the combo
of tektoncd#375 and tektoncd#443, but now that we've removed the extra log PVC in tektoncd#443
we shouldn't run into this issue anymore :D

test/e2e-tests-yaml.sh

@@ -33,12 +33,7 @@ install_pipeline_crd
 
 # Run the tests
 failed=0
-# FIXME(vdemeester) add pipelinerun to the test…
-# They are currently block by
-# - https://github.com/knative/build-pipeline/issues/375
-# - https://github.com/knative/build-pipeline/pull/443
-# for test in taskrun pipelinerun; do
-for test in taskrun; do
+for test in taskrun pipelinerun; do
   header "Running YAML e2e tests for ${test}s"
   if ! run_yaml_tests ${test}; then
     echo "ERROR: one or more YAML tests failed"