dockerfiles: upgrade to ubuntu:20.04; some chore (#3828)

* dockerfiles: upgrade to ubuntu:20.04; some chore

* dockerfiles: fq container names

polkadot/bridges/deployments/BridgeDeps.Dockerfile

@@ -2,7 +2,7 @@
 #
 # This image is meant to be used as a building block when building images for
 # the various components in the bridge repo, such as nodes and relayers.
-FROM ubuntu:20.04
+FROM docker.io/library/ubuntu:20.04
 
 ENV LAST_DEPS_UPDATE 2021-04-01
 ENV DEBIAN_FRONTEND=noninteractive

polkadot/bridges/deployments/bridges/poa-rialto/Front-end.Dockerfile

@@ -1,4 +1,4 @@
-FROM node:12 as build-deps
+FROM docker.io/library/node:12 as build-deps
 
 # install tools and dependencies
 RUN set -eux; \
@@ -19,7 +19,7 @@ ENV EXPECTED_ETHEREUM_NETWORK_ID $EXPECTED_ETHEREUM_NETWORK_ID
 RUN yarn build:docker
 
 # Stage 2 - the production environment
-FROM nginx:1.12
+FROM docker.io/library/nginx:1.12
 COPY --from=build-deps /usr/src/bridge-ui/nginx/*.conf /etc/nginx/conf.d/
 COPY --from=build-deps /usr/src/bridge-ui/dist /usr/share/nginx/html
 EXPOSE 80

polkadot/bridges/deployments/monitoring/GrafanaMatrix.Dockerfile

@@ -1,4 +1,4 @@
-FROM ruby:alpine
+FROM docker.io/library/ruby:alpine
 
 RUN apk add --no-cache git
 

polkadot/bridges/deployments/networks/OpenEthereum.Dockerfile

@@ -1,4 +1,4 @@
-FROM ubuntu:xenial AS builder
+FROM docker.io/library/ubuntu:xenial AS builder
 
 # show backtraces
 ENV RUST_BACKTRACE 1
@@ -60,7 +60,7 @@ WORKDIR /openethereum
 RUN cargo build --release --verbose
 RUN strip ./target/release/openethereum
 
-FROM ubuntu:xenial
+FROM docker.io/library/ubuntu:xenial
 
 # show backtraces
 ENV RUST_BACKTRACE 1