admin: stats_handler_speed_test destruction seems to hang due to per-host info

When I run stats-handler_speed_test it takes a surprising amount of time to initialize, and even longer to finish (return to the prompt).

Something n^2 might be happening in the mocks destruct sequence, or maybe a lock issue.

https://github.com/envoyproxy/envoy/pull/32197 enables a workaround by only initializing the host info when called for by a test, so someone can use a regex to run only the 'disabled' tests. With the above PR:
```
time ./bazel-bin/test/server/admin/stats_handler_speed_test --'benchmark_filter=disabled'
...
13.965u 0.047s 0:14.01 99.9% 0+0k 0+0io 0pf+0w
```

whereas by default:
```
time ./bazel-bin/test/server/admin/stats_handler_speed_test
...
(appears to hang after reporting all results: will update when it finishes)
```