Also, fix the case where we didn't use --network with EXPOSE_TCP,
as reported by @theborakompanioni:
```
I get Wrong network! Our Bitcoin backend is running on 'regtest', but we expect 'main'. with LIGHTNINGD_NETWORK := regtest when param --network is not provided.
```
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
Before this, docker image will never detects that
`lightning-rpc` was created if it is running in regtest
or testnet, because the file will be created under
subfolder for each network name, and entrypoint does not
check "lightning-rpc" file in those folders.
By specifying `LIGHTNINGD_NETWORK` environment var
in dockerfile, we can now check correct path.
Changelog-Added: Docker build now includes `LIGHTNINGD_NETWORK` ENV variable which defaults to "bitcoin". An user can override this (e.g. by `-e` option in `docker run`) to run docker container in regtest or testnet or any valid argument to `--network`.
This is based on @NicolasDorier's excellent proposal for a Dockerfile, sans the
writing of a config file.
Co-authored-by: Nicolas Dorier <nicolas.dorier@gmail.com>
Co-authored-by: Christian Decker <decker.christian@gmail.com>
Signed-off-by: Christian Decker <decker.christian@gmail.com>
