Move Docker scripts (#138)

Just reorganizing

docker/scripts/build_docker.sh

@@ -0,0 +1,21 @@
+#!/usr/bin/env bash
+
+set -e
+
+cd "$(cd "$(dirname "$0")" && git rev-parse --show-toplevel)"
+
+dockerfile="$1"
+if [ -z "$dockerfile" ]; then
+    dockerfile="./docker/test-parachain-collator.dockerfile"
+else
+    shift 1
+fi
+image_name="$(basename "$dockerfile" | rev | cut -d. -f2- | rev)"
+
+echo "building $dockerfile as $image_name..."
+
+time docker build \
+    -f "$dockerfile" \
+    -t "$image_name":latest \
+    "$@" \
+    .