When Consul Connect just works, it's wonderful. When it doesn't work it
can be exceeding difficult to debug: operators have to check task
events, Nomad logs, Consul logs, Consul APIs, and even then critical
information is missing.
Using Consul to generate a bootstrap config for Envoy is notoriously
difficult. Nomad doesn't even log stderr, so operators are left trying
to piece together what went wrong.
This patch attempts to provide *maximal* context which unfortunately
includes secrets. **Secrets are always restricted to the secrets/
directory.** This makes debugging a little harder, but allows operators
to know exactly what operation Nomad was trying to perform.
What's added:
- stderr is sent to alloc/logs/envoy_bootstrap.stderr.0
- the CLI is written to secrets/.envoy_bootstrap.cmd
- the environment is written to secrets/.envoy_bootstrap.env as JSON
Accessing this information is unfortunately awkward:
```
nomad alloc exec -task connect-proxy-count-countdash b36a cat secrets/.envoy_bootstrap.env
nomad alloc exec -task connect-proxy-count-countdash b36a cat secrets/.envoy_bootstrap.cmd
nomad alloc fs b36a alloc/logs/envoy_bootstrap.stderr.0
```
The above assumes an alloc id that starts with `b36a` and a Connect
sidecar proxy for a service named `count-countdash`.
If the alloc is unable to start successfully, the debugging files are
only accessible from the host filesystem.
