Consider defaulting e2e to parallel when in non-destructive mode

[johnSchnake]

When in non-destructive-conformance mode we currently run in series which makes the tests take a substantial amount of time. I'm not sure how flakey tests get in parallel though.

Recommend investigating test grid and seeing if those are in parallel.

Would also need #1519 to be completed before we do this.

[stale[bot]]

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