tests (e2e/cli/cache_search): make the test more resilient: the caching is triggered by `li.blog.get`, but it is done in parallel without blocking the command, thus there is a possibility that the data is not yet in cache when the following test is done. A loop with delay is done, to be sure that cache is filled before doing the assertion.

this certificates are used to enable TLS during tests. Those must be the same as in
backend_e2e (they are generated there)