Add in wait for pods to be initiated

Created by: davejrt

Adds in a small delay for pods to be created (not ready) by the kubelet. I saw in local testing that some pods were very slightly behind the rest. Given how quickly this script runs through commands it's possible the pod hasn't been created before we check that it's ready.

fixes https://github.com/sourcegraph/sourcegraph/issues/32403

Test plan

Green build on main-dry-run https://buildkite.com/sourcegraph/sourcegraph/builds/138656#bc3329ff-daf6-4616-a44a-fa670cff5afa/1