scripts: install bitcoind binary from docker image

Because the bitcoind mirror is extremely slow, we spend at least 2 to 3
minutes of each bitcoind related test on just downloading the binary. We
can achieve the same result by just pulling the docker image and
extracting the binary from that.

scripts/install_bitcoind.sh

@@ -2,17 +2,9 @@
 
 set -ev
 
-export BITCOIND_VERSION=0.20.0
-
-if sudo cp ~/bitcoin/bitcoin-$BITCOIND_VERSION/bin/bitcoind /usr/local/bin/bitcoind
-then
-        echo "found cached bitcoind"
-else
-        mkdir -p ~/bitcoin && \
-        pushd ~/bitcoin && \
-        wget https://bitcoin.org/bin/bitcoin-core-$BITCOIND_VERSION/bitcoin-$BITCOIND_VERSION-x86_64-linux-gnu.tar.gz && \
-        tar xvfz bitcoin-$BITCOIND_VERSION-x86_64-linux-gnu.tar.gz && \
-        sudo cp ./bitcoin-$BITCOIND_VERSION/bin/bitcoind /usr/local/bin/bitcoind && \
-        popd
-fi
+BITCOIND_VERSION=${BITCOIN_VERSION:-0.20.1}
 
+docker pull ruimarinho/bitcoin-core:$BITCOIND_VERSION
+CONTAINER_ID=$(docker create ruimarinho/bitcoin-core:$BITCOIND_VERSION)
+sudo docker cp $CONTAINER_ID:/opt/bitcoin-$BITCOIND_VERSION/bin/bitcoind /usr/local/bin/bitcoind
+docker rm $CONTAINER_ID