Add healthcheck for adminer.

adminer/Dockerfile

@@ -0,0 +1,5 @@
+FROM adminer
+
+COPY docker-healthcheck /usr/local/bin/
+
+HEALTHCHECK CMD ["docker-healthcheck"]

adminer/docker-healthcheck

@@ -0,0 +1,10 @@
+#!/bin/sh
+set -eo pipefail
+
+host="$(hostname -i)"
+
+if curl -sS "http://$host:8080"; then
+    exit 0
+fi
+
+exit 1