Take LIGHTNINGD_NETWORK env variable in Dockerfile.

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`.

Dockerfile

@@ -88,6 +88,7 @@ RUN apt-get update && apt-get install -y --no-install-recommends socat inotify-t
 ENV LIGHTNINGD_DATA=/root/.lightning
 ENV LIGHTNINGD_RPC_PORT=9835
 ENV LIGHTNINGD_PORT=9735
+ENV LIGHTNINGD_NETWORK=bitcoin
 
 RUN mkdir $LIGHTNINGD_DATA && \
     touch $LIGHTNINGD_DATA/config

tools/docker-entrypoint.sh

@@ -2,18 +2,20 @@
 
 : "${EXPOSE_TCP:=false}"
 
+networkdatadir="${LIGHTNINGD_DATA}/${LIGHTNINGD_NETWORK}"
+
 if [ "$EXPOSE_TCP" == "true" ]; then
     set -m
     lightningd "$@" &
 
     echo "C-Lightning starting"
     while read -r i; do if [ "$i" = "lightning-rpc" ]; then break; fi; done \
-    < <(inotifywait  -e create,open --format '%f' --quiet "$LIGHTNINGD_DATA" --monitor)
+    < <(inotifywait -e create,open --format '%f' --quiet "${networkdatadir}" --monitor)
     echo "C-Lightning started"
     echo "C-Lightning started, RPC available on port $LIGHTNINGD_RPC_PORT"
 
-    socat "TCP4-listen:$LIGHTNINGD_RPC_PORT,fork,reuseaddr" "UNIX-CONNECT:$LIGHTNINGD_DATA/lightning-rpc" &
+    socat "TCP4-listen:$LIGHTNINGD_RPC_PORT,fork,reuseaddr" "UNIX-CONNECT:${networkdatadir}/lightning-rpc" &
     fg %-
 else
-    exec lightningd "$@"
+    exec lightningd --network="${LIGHTNINGD_NETWORK}" "$@"
 fi