flake: envoy integration test gateways-local

This is seen, for example, in [this CI run](https://app.circleci.com/pipelines/github/hashicorp/consul/7993/workflows/dded33cd-b8ba-42a8-95fd-0f5c1846ed25/jobs/144816/parallel-runs/0/steps/0-105).

```
CASE gateways-local, envoy 1.11.2: Going to remove envoy_verify-primary_1
Removing envoy_verify-primary_1 ...
envoy_consul-primary_1 is up-to-datemdone
Creating envoy_verify-primary_1 ...
Attaching to envoy_verify-primary_12mdone
verify-primary_1 | 1..9
verify-primary_1 | ok 1 s1 proxy is running correct version
verify-primary_1 | ok 2 s1 proxy admin is up on :19000
verify-primary_1 | ok 3 gateway-primary proxy admin is up on :19002
verify-primary_1 | ok 4 s1 proxy listener should be up and have right cert
verify-primary_1 | ok 5 s1 upstream should have healthy endpoints for s2
verify-primary_1 | ok 6 gateway-primary should have healthy endpoints for secondary
verify-primary_1 | not ok 7 s1 upstream should be able to connect to s2
verify-primary_1 | # (in test file /workdir/primary/bats/verify.bats, line 32)
verify-primary_1 | # `[ "$status" -eq 0 ]' failed
verify-primary_1 | ok 8 s1 upstream made 1 connection
verify-primary_1 | ok 9 gateway-primary is used for the upstream connection
envoy_verify-primary_1 exited with code 1
Aborting on container exit...
⨯ FAIL
```

Start with the gateways-local failure in the linked CI run and inspect primary/bats/verify.bats at line 32, where the s1-to-s2 connection check fails. Reproduce the case and compare the failing connection with the surrounding checks; done means the test passes reliably without losing the expected gateway connection.

Written by the indexing model from the issue text.