Install latest pipeline release in tests

This will make sure we are installing latest
pipeline release instead of the first tag on releases

This will fix the e2e tests failures observed in
#1754 with error message
like `json: unknown field "artifacts"`

Author: piyush-garg

test/e2e-common.sh

@@ -35,7 +35,7 @@ function install_pipeline_crd() {
   if [[ -n ${RELEASE_YAML} ]];then
 	  latestreleaseyaml=${RELEASE_YAML}
   else
-    latestreleaseyaml=$(curl -s https://api.github.com/repos/tektoncd/pipeline/releases|python -c "import sys, json;x=json.load(sys.stdin);ass=x[0]['assets'];print([ x['browser_download_url'] for x in ass if x['name'] == 'release.yaml'][0])")
+    latestreleaseyaml="https://storage.googleapis.com/tekton-releases/pipeline/latest/release.yaml"
   fi
   [[ -z ${latestreleaseyaml} ]] && fail_test "Could not get latest released release.yaml"
   kubectl apply -f ${latestreleaseyaml} ||