e2e: remove possible race condition when parallel running

[hj-johannes-lee]

Theoretically, ginkgo specs can run specs in parallel. In our current e2e tests (found in PR #1472, but will not be fixed in the PR), if specs run in parallel, two different processes (plugin without using operator VS plugin with using operator) may possibly require the same device resources at the same time.

We are running e2e tests with go test ~~, which does not support parallel running. So, there are no visible errors, but it should be improved.