Nomad not GCing old connect sidecar proxy containers

While upgrading a VPS to v1.1.0-beta (from v1.0.4) yesterday I noticed a lot of old connect sidecar proxy images lingering around. These should get cleaned up like any other tasks. One thing to note is `sudo reboot` is the usual way nomad gets restarted on this machine.

```
$ docker ps -a
CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAMES
f253bd836433 envoyproxy/envoy:v1.16.0 "/docker-entrypoint.…" 2 weeks ago Up 2 weeks connect-proxy-caddy-6cd4582e-f107-29da-fce7-e244a3616ca8
253ab9078177 gcr.io/google_containers/pause-amd64:3.1 "/pause" 2 weeks ago Up 2 weeks nomad_init_6cd4582e-f107-29da-fce7-e244a3616ca8
db1c325dd466 envoyproxy/envoy:v1.16.0 "/docker-entrypoint.…" 2 weeks ago Up 2 weeks connect-proxy-ubs-32af591a-b24f-7742-1bdb-272577af55e5
dac2847f8381 gcr.io/google_containers/pause-amd64:3.1 "/pause" 2 weeks ago Up 2 weeks nomad_init_32af591a-b24f-7742-1bdb-272577af55e5
43cca8c2cf4e envoyproxy/envoy:v1.16.0 "/docker-entrypoint.…" 2 weeks ago Up 2 weeks connect-proxy-hclfmt-f500e4fb-5054-4c03-899a-f8bb551d536d
57e528fdcc2a gcr.io/google_containers/pause-amd64:3.1 "/pause" 2 weeks ago Up 2 weeks nomad_init_f500e4fb-5054-4c03-899a-f8bb551d536d
0b0c9d6c05e4 envoyproxy/envoy:v1.16.0 "/docker-entrypoint.…" 2 weeks ago Up 2 weeks connect-proxy-mod-redirect-b9231645-14ea-2ee4-66ac-da196a36faf6
7b4836b5f064 gcr.io/google_containers/pause-amd64:3.1 "/pause" 2 weeks ago Up 2 weeks nomad_init_b9231645-14ea-2ee4-66ac-da196a36faf6
00ebf65b1785 envoyproxy/envoy:v1.16.0 "/docker-entrypoint.…" 3 weeks ago Exited (137) 2 weeks ago connect-proxy-caddy-e2c9a50d-027b-28d1-54f0-80f47c7cb922
98d04623cf23 envoyproxy/envoy:v1.16.0 "/docker-entrypoint.…" 3 weeks ago Exited (137) 2 weeks ago connect-proxy-mod-redirect-bad304f8-28ff-e15e-d405-7ff25690a2b9
7a9b36ecdacf envoyproxy/envoy:v1.16.0 "/docker-entrypoint.…" 3 weeks ago Exited (137) 2 weeks ago connect-proxy-hclfmt-18aca177-e1e1-9ae1-ed71-bace2801fa17
01243b11ae00 envoyproxy/envoy:v1.16.0 "/docker-entrypoint.…" 3 weeks ago Exited (137) 2 weeks ago connect-proxy-ubs-ec6a3eb9-d636-7448-5ecf-7d53f1c19ac9
ff49aad9a75a envoyproxy/envoy:v1.16.0 "/docker-entrypoint.…" 4 weeks ago Exited (137) 3 weeks ago connect-proxy-ubs-d06e403f-b2f8-3fe2-cade-5b3f904f968e
e6eedfdd3266 envoyproxy/envoy:v1.16.0 "/docker-entrypoint.…" 4 weeks ago Exited (137) 3 weeks ago connect-proxy-caddy-c1a19c31-7835-6041-fb78-c01f48d0b09a
3a9ec48f078d envoyproxy/envoy:v1.16.0 "/docker-entrypoint.…" 4 weeks ago Exited (137) 3 weeks ago connect-proxy-hclfmt-eae9fafb-9432-faec-4e7c-122e88b67c21
fa2d0c416feb envoyproxy/envoy:v1.16.0 "/docker-entrypoint.…" 4 weeks ago Exited (137) 3 weeks ago connect-proxy-mod-redirect-5c70ae62-b77f-2496-dbdc-ba276b419832
fe3bcea74ab2 envoyproxy/envoy:v1.16.0 "/docker-entrypoint.…" 5 weeks ago Exited (137) 4 weeks ago connect-proxy-hclfmt-b539bbf5-72ab-4bb1-6170-c3775bcfb84f
59cfa975192c envoyproxy/envoy:v1.16.0 "/docker-entrypoint.…" 5 weeks ago Exited (137) 4 weeks ago connect-proxy-ubs-ddf3f60d-7352-717b-5370-a2d66e9d7037
b4e79a8501bc envoyproxy/envoy:v1.16.0 "/docker-entrypoint.…" 5 weeks ago Exited (137) 4 weeks ago connect-proxy-caddy-a5c4494b-1234-ca26-c0b3-4bc28514af84
bb4d1b270388 envoyproxy/envoy:v1.16.0 "/docker-entrypoint.…" 5 weeks ago Exited (137) 4 weeks ago connect-proxy-mod-redirect-96e66b8b-85ee-7748-bba8-547dc6489b40
21768eef2735 envoyproxy/envoy:v1.16.0 "/docker-entrypoint.…" 2 months ago Exited (137) 5 weeks ago connect-proxy-hclfmt-86543d62-1500-29e3-9313-1f27207068d4
1d877a3b9369 envoyproxy/envoy:v1.16.0 "/docker-entrypoint.…" 2 months ago Exited (137) 5 weeks ago connect-proxy-ubs-055eafb2-57fc-fbe9-26e0-a7b911dce734
34c0e46be1ca envoyproxy/envoy:v1.16.0 "/docker-entrypoint.…" 2 months ago Exited (137) 5 weeks ago connect-proxy-mod-redirect-98ccef05-48cc-6483-44aa-5523a0853efb
a8fe5fdff3c2 envoyproxy/envoy:v1.16.0 "/docker-entrypoint.…" 2 months ago Exited (137) 5 weeks ago connect-proxy-caddy-7057d6f8-b3d7-e2f8-c4ae-9d58af4971c2
```

The report identifies Docker containers named connect-proxy-* and nomad_init_* but no source file or test. Start by tracing Nomad's Docker task cleanup path for Connect sidecars and verify behavior around a restart; done means exited old sidecar containers are removed while active proxies remain.

Written by the indexing model from the issue text.