Integrations tests should be regularly run with assertions disabled

[mark-vieira]

As discussed here we lack coverage for detecting if we are implicitly relying on side effects in assertions due to the fact that we don't run external cluster tests w/ assertions disabled. We have found issues in the past in production related specifically to side effects in assertion statements.

We should add a periodic build for catching things like this which simply runs our external cluster tests against a cluster configured as it would be in production, w/o -ea.

[elasticmachine]

Pinging @elastic/es-delivery (Team:Delivery)