Refactor Dockerfile [skip ci]

Author: Claudio Raimondi

Dockerfile

@@ -46,7 +46,7 @@ RUN tar xzf ${BITCOIN_TARBALL} --strip-components=1
 ARG LITECOIN_VERSION=0.16.3
 ARG LITECOIN_BASE_URL=https://download.litecoin.org/litecoin-${LITECOIN_VERSION}
 ARG LITECOIN_URL=${LITECOIN_BASE_URL}/linux
-ARG LITECOIN_TARBALL=litecoin-${LITECOIN_VERSION}-${TARBALL_ARCH}.tar.gz
+ARG LITECOIN_TARBALL=litecoin-${LITECOIN_VERSION}-${TARGET_ARCH_TARBALL}.tar.gz
 
 WORKDIR /opt/litecoin
 
@@ -186,8 +186,6 @@ COPY --from=builder       /tmp/lightning_install/           /usr/local/
 
 COPY tools/docker-entrypoint.sh    /entrypoint.sh
 
-#TODO: user creation. user permissions on volume.
-
 ENV LIGHTNINGD_DATA=/root/.lightning
 ENV LIGHTNINGD_RPC_PORT=9835
 ENV LIGHTNINGD_PORT=9735