Apparently conformance tests have to run serially

There are 10+ conformance tests marked [Serial], So we can't run things
in parallel by default.

Change-Id: I58afbb356899fb38caf4f9f6704bfb47f745b338

Author: dims

cluster/images/conformance/conformance-e2e.yaml

@@ -65,7 +65,7 @@ spec:
     - name: E2E_PROVIDER
       value: "local"
     - name: E2E_PARALLEL
-      value: "y"
+      value: "1"
     volumeMounts:
     - name: output-volume
       mountPath: /tmp/results