Nexus: Resource lock nexus examples

[prckent]

Proposed changes

Speculative update to serialize nexus example tests and avoid potential race condition. Result should be no nexus examples sporadically failing on cdash. Only the example tests are serialized so the effect on overall test runtime is minimal.

What type(s) of changes does this code introduce?

• Bugfix
• Testing changes (e.g. new unit/integration/performance tests)

Does this introduce a breaking change?

• No

What systems has this change been tested on?

Checklist

• Yes. This PR is up to date with current the current state of 'develop'
• NA. Code added or changed in the PR has been clang-formatted
• NA. This PR adds tests to cover any new code, or to catch a bug that is being fixed
• NA. Documentation has been added (if appropriate)

[jtkrogel]

LGTM. This should capture only the user example tests.

[ye-luo]

Test this please

[ye-luo]

Hopefully this will be all what we need.