Tolerate errors from Find for tasks with WarnIfInsufficientAccess

[justinsb]

We glog.Warning a message, and we record a structured warning for future
use, but we allow operation to continue.

[justinsb]

@chrislovecnm I think you'll like this ... this is how I envisaged we would tolerate errors for just-validate tasks - we're just glog.Warning at the moment, but starting to collect warnings as well for a future structured presentation.

Should also help with GCE ... we don't have the ACL permissions either :-(
https://storage.googleapis.com/kubernetes-jenkins/logs/ci-kubernetes-e2e-kops-gce/406/build-log.txt

But it's a good test case for locked-down environments. I don't like defaulting to WarnIfInsufficientAccess for this task, but it's better than the immediate alternative which is just ripping it out entirely. If this works out, I think I'll tweak it so that the e2e tests opt in to WarnIfInsufficientAccess eventually (though I haven't fully thought that through yet!)

[justinsb]

/retest

[chrislovecnm]

/lgtm

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